Heart

Parent: Global AI Hub Research Corpus · Published reference · snapshot 2026-08-31

The heart is a hollow muscular organ of somewhat conical form lying between the lungs in the middle mediastinum, enclosed in the pericardium; it is the central organ of the blood vascular system, pumping blood through the arteries by its contraction, and is divided by septa into right and left halves, each with an atrium and a ventricle. One source (Gray's Anatomy 1918, Angiology) covers its definition, structure (chambers, valves, wall and conduction tissue, coronary vessels, pericardium), mechanism (development, cardiac cycle, fetal circulation), size and cycle timings, and the two malformations the text names.

These notes link each claim to its source. Some citations identify archived research reports that are no longer hosted on this site. A published reference means the content is available; it does not certify independent review or accuracy.Read the editorial policy and follow the sources before relying on a claim.

Definitions

The right atrioventricular orifice is the large oval aperture of communication between the right atrium and ventricle. Situated at the base of the ventricle, it measures about 4 cm. in diameter and is surrounded by a fibrous ring, covered by the lining membrane of the heart; it is considerably larger than the correspond- ing aperture on the left side, being sufficient to admit the ends of four fingers It is guarded by the tricuspid valve. [source]
The atrioventricular opening (tricuspid orifice) is the large oval aperture of com- munication between the atrium and the ventricle; it will be described with the right ventricle. [source]
The left atrioventricular opening is the aperture between the left atrium and ventricle, and is rather smaller than the corresponding opening on the right side. [source]
The limbus fossae ovalis (ayiniilus ovalis) is the prominent oval margin of the fossa ovalis. It is most distinct above and at the sides of the fossa; below, it is deficient. A small slit-like valvular opening is occasionally found, at the upper margin of the fossa, leading upward beneath the limbus, into the left atrium ; it is the remains of the fetal aperture between the two atria. [source]
The serous pericardium is, as already stated, a closed sac which lines the fibrous pericardium and is invaginated by the heart; it therefore consists of a visceral and a parietal portion. The visceral portion, or epicardium, covers the heart and the great vessels, and from the latter is continuous with the parietal layer which lines the fibrous pericardium. The portion which covers the vessels is arranged in the form of two tubes. The aorta and pulmonary artery are enclosed in one tube, the arterial mesocardium. The superior and inferior vence cavoe and the four puhnonary veins are enclosed in a second tube, the venous mesocardium, the attachment of which to the parietal layer presents the shape of an inverted U. The cul-de-sac enclosed between the hmbs of the U Hes behind the left atrium and is known as the oblique sinus, while the passage between the venous and arterial niesocardia — i. e., between the aorta and pulmonary artery in front and the atria behind — is termed the transverse sinus. [source] — epicardium = visceral serous pericardium
The pericardium (Fig. 489) is a conical fibro-serous sac, in which the heart and the roots of the great vessels are contained. It is placed behind the sternum and the cartilages of the third, fourth, fifth, sixth, and seventh ribs of the left side, in the mediastinal cavity. [source]
The heart is a hollow muscular organ of a somewhat conical form; it lies between the lungs in the middle mediastinum and is enclosed in the pericardium (Fig. 490). It is placed obliquely in the chest behind the body of the sternum and adjoining parts of the rib cartilages, and projects farther into the left than into the right half of the thoracic cavity, so that about one-third of it is situated on the right and two-thirds on the left of the median plane. [source]
The heart is the central organ of the blood vascular system, and consists of a hollow muscle; by its contraction the blood is pumped to all parts of the body through a complicated series of tubes, termed arteries. The arteries undergo enormous ramification in their course throughout the body, and end in minute vessels, called arterioles, which in their turn open into a close-meshed network of microscopic vessels, termed capillaries. After the blood has passed through the capillaries it is collected into a series of larger vessels, called veins, by which it is returned to the heart. The passage of the blood through the heart and blood- vessels constitutes what is termed the circulation of the blood, of which the following is an outline. [source]
Structure of the Pericardiiun. — Although the pericardium is usually described as a single sac, an examination of its structure shows that it consists essentially of two sacs intimately connected with one another, but totally different in structure. The outer sac, known as the fibrous peri- cardium, consists of fibrous tissue. The inner sac, or serous pericardium, is a deUcate mem- brane which lies within the fibrous sac and lines its walls; it is composed of a single layer of [source] — fibrous and serous pericardium

Structure and components

The fibrous rings surround the atrioventricular and arterial orifices, and are stronger upon the left than on the right side of the heart. The atrioventricular rings serve for the attachment of the muscular fibers of the atria and ventricles, and for the attachment of the bicuspid and tricuspid valves. The left atrioventricular ring is closely connected, bj' its right margin, with the aortic arterial ring; between these and the right atrioventricular ring is a triangular mass of fibrous tissue, the trigonum fibrosum, which represents the os cordis seen in the heart of some of the larger animals, as the ox and elephant. Lasth', there is the tendinous band, already referred to, the posterior surface of the conus arteriosus. [source]
The atrioventricular bundle of His iFig. 501), is the only direct muscular connection known to exist between the atria and the ventricles. Its cells differ from ordinary cardiac muscle cells in being more spindle-shaped. They are, moreover, more loosely arranged and have a richer vascu- lar supply than the rest of the heart muscle. It arises in connection with two small collections of spindle-shaped cells, the sinoatrial and atrioventricular nodes. The sinoatrial node is situated on the anterior border of the opening of the superior vena cava ; from its strands of fusiform fibers run under the endocardiiun of the wall of the atrium to the atrioventricular node. The atrioventricular node lies near the orifice of the coronary sinus in the annular and septal fibers of the right atrium; from it the atrioventricular bundle passes forward in the lower part of the membranous septum, and divides into right and left fascicuh. These run down in the right and left ventricles, one on either side of the ventricular septum, covered by endocardium. In the lower parts of the ventricles they break up into numerous strands which end in the papillary muscles and in the ventricular muscle generally. The greater portion of the atrioventricular bundle consists of narroWj somewhat fusifgrm fibers, but its terminal strands are composed of Pm-kinje fibers. [source]
Right Ventricle (ventriculus dexter). — The right ventricle is triangular in form, and extends from the right atrium to near the apex of the heart. Its antero- superior surface is rounded and convex, and forms the larger part of the sterno- costal surface of the heart. Its under surface is flattened, rests upon the dia- phragm, and forms a small part of the diaphragmatic surface of the heart. Its posterior wall is formed by the ventricular septum, which bulges into the right ventricle, so that a transverse section of the cavity presents a semilunar outline. Its upper and left angle forms a conical pouch, the conus arteriosus, from which the pulmonary artery arises. A tendinous band, which may be named the tendon of the conus arteriosus, extends upward from the right atrioventt».^ilir fibrous ring and connects the posterior surface of the conus arteriosus to the aoirta. The wall of the right ventricle is thinner than that of the left, the proportion betwet*;! them being as 1 to 3; it is thickest at the base, and gradually becomes thinnei* toward the apex. The cavity equals in size that of the left ventricle, and is capable of containing about 85 c.c. \ [source]
The fibers of the ventricles are arranged in a complex manner, and various accounts have been given of their course and connections; the following description is based on the work of McCallum.i They consist of superficial and deep layers, all of which, with the exception of two, are inserted into the papillary muscles of the ventricles. The superficial layers consist of the following: (a) Fibers which spring from the tendon of the conus arteriosus and sweep downward and toward the left across the anterior longitudinal sulcus and around the apex of the heart, where they pass upward and inward to terminate in the papillary muscles of the left ventricle; those arising from the upper half of the tendon of the conus arteriosus pass to the anterior papillary muscle, those from the lower half to the posterior papillary muscle and the papillary muscles of the septum. (6) Fibers which arise from the right atrioventricular ring and run diagonall}' across the diaphragmatic surface of the right ventricle and around its right border on to its costosternal sm'face, where they dip beneath the fibers just described, and, crossing the anterior longitudinal sulcus, wind around the apex of the heart and end in the posterior papillary muscle of the left ventricle, (c) Fibers which spring from the left atrioventricular ring, and, crossing the posterior longitudinal sulcus, pass successively into the right ventricle and end in its papillary muscles. The deep layers are three in number; they arise in the papillary muscles of one ventricle and, curving in an S-shaped manner, turn in at the longitudinal sulcus and end in the papillary muscles of the other ventricle. The layer which is most superficial in the right ventricle hes next the lumen of the left, and vice versa. Those of the first layer almost encircle the right ventricle and, crossing in the septum to the left, unite with the superficial fibers from the right atrioventricular ring to form the posterior papillary muscle. Those of the second layer have a less extensive com-se in the wall of the right ventricle, and a correspondingly greater course in the left, where they join with the superficial fibers from the anterior half of the tendon of the conus arteriosus to form the papillary muscles of the septum. Those of the third layer pass almost entirely around the left ventricle and unite with the superficial fibers from the lower half of the tendon of the conus arteriosus to form the anterior papillary muscle. Besides the layers just described there are two bands which do not end in papiL'ar}' muscles. One springs from the right atrioventricular ring and crosses in the atrioventricular septum; it then encircles the deep layers of the left ventricle and ends in the left atrioventricular ring. The second band is apparently confined to the left ventricle; it is attached to the left atrioventricular ring, and encircles the portion of the ventricle adjacent to the aortic orifice. [source]
The coronary sinus opens into the atrium, between the orifice of the inferior vena cava and the atrioventricular opening. It returns blood from the substance of the heart and is protected by a semicircular valve, the valve of the coronary sinus {valve of Thebesius). [source]
The tricuspid valve {valvula tricuspidalis) (Figs. 493, 495) consists of three some- what triangular cusps or segments. The largest cusp is interposed between the atrioventricular orifice and the conus arteriosus and is termed the anterior or infundib- ular cusp. A second, the posterior or marginal cusp, is in relation to the right margin of the ventricle, and a third, the medial or septal cusp, to the ventricular septum. They are formed b}- duplicatures of the lining membrane of the heart, strengthened [source]
The aortic opening is a circular aperture, in front and to the right of the atrio- ventricular, from which it is separated by, the anterior cusp of the bicuspid valve. Its orifice is guarded by the aortic semilunar valves. The portion of the ventricle immediately below the aortic orifice is termed the aortic vestibule, and possesses fibrous instead of muscular walls. [source]
they form ;i considerable portion of the moderator band and also appear as gelatinous-looking strands on the inner walls of the atria and ventricles. They also occur in the human heart asso- ciated with the terminal distributions of the bundle of His. The fibers are very much larger in size than the cardiac cells and differ from them in several ways. In longitudinal section they are quadrilateral in shape, being about twice as long as they are broad. The central portion of each fiber contains one or more nuclei and is made up of granular protoplasm, with no indication of Ptriations, while the peripheral portion is clear and has cUstinct transverse striations. The fibers are intimately connected with each other, possess no definite sarcolcmma, and do not branch. [source]
The inferior vena cava, larger than the superior, returns the blood from the lower half of the body, and opens into the lowest part of the atrium, near the atrial septum, its orifice being directed upward and backward, and guarded by a rudimentary valve, the valve of the inferior vena cava (Eustachian valve). The blood entering the atrium through the superior vena cava is directed downward and forward, i. e., toward the atrioventricular orifice, while that entering through the inferior vena cava is directed upward and backward, toward the atrial septum. This is the normal direction of the two currents in fetal life. [source]
The valve of the inferior vena cava (vahula venae cava' inferioris [Eustachii]; Eustachian valve) is situated in front of the orifice of the inferior vena cava. It is semilunar in form, its convex margin being attached to the anterior margin of the orifice; its concave margin, which is free, ends in two cornua, of which the left is continuous with the anterior edge of the limbus fossie ovalis while the right is lost on the wall of the atrium. The valve is formed by a duplicature of the lining membrane of the atrium, containing a few muscular fibers, hi the fetus this valve is of large size, and serves to direct the blood from the inferior vena cava, through the foramen ovale, into the left atrium. In the adult it occa- sionally persists, and may assist in preventing the reflux of blood into the inferior vena cava; more commonly it is small, and may present a cribriform or filamentous appearance; sometimes it is altogether wanting. [source]
by intervening layers of fibrous tissue: their central parts are thick and strong, their marginal portions thin and translucent, and in the angles between the latter small intermediate segments are sometimes seen. Their bases are attached to a fibrous ring surrounding the atrioventricular orifice and are also joined to each other so as to form a continuous annular membrane, while their apices project into the ventricular cavity. Their atrial surfaces, directed toward the blood current from the atrium, are smooth; their ventricular surfaces, directed toward the wall of the ventricle, are rough and irregular, and, together with the apices and margins of the cusps, give attachment to a number of delicate tendinous cords, the chordae tendineae. [source]
The trabeculse cameae (columrur carnecr) are rounded or irregular muscular columns which project from the whole of the inner surface of the ventricle, with the exception of the conus arteriosus. They are of three kinds: some are attached along their entire length on one side and merely form prominent ridges, others are fixed at their extremities but free in the middle, while a third set {muscidi papillares) are continuous by their bases with the wall of the ventricle, while their apices give origin to the chordiv tendineiie which pass to be attached to the seg- ments of the tricuspid valve. There are two papillary muscles, anterior and pos- terior: of these, the anterior is the larger, and its chorda? tendinccT are connected with the anterior and posterior cusps of the valve: the posterior papillary muscle sometimes consists of two or three parts; its chordae tendineffi are connected . with the posterior and medial cusps. In addition to these, some chorda? tendineee spring directly from the ventricular septum, or from small papillary eminences on it, and pass to the anterior and medial cusps. A muscular band, well-marked in sheep and some other animals, frequently extends from the base of the anterior papillary muscle to the ventricular septum. From its attachments it may assist in preventing overdistension of the ventricle, and so has been named the moderator band. [source]
The bicuspid or mitral valve (valvula bicuspidalis [metralis]) (Figs. 495, 496) is attached to the circumference of the left atrioventricular orifice in the same way that the tricuspid valve is on the opposite side. It consists of two triangular cusps, formed by duplicatures of the lining membrane, strengthened by fibrous tissue, and containing a few muscular fibers. The cusps are of unequal size, and are larger, thicker, and stronger than those of the tricuspid valve. The larger cusp is placed in front and to the right between the atrioventricular and aortic orifices, and is known as the anterior or aortic cusp ; the smaller or posterior cusp is placed behind and to the left of the opening. Two smaller cusps are usually found at the angles of junction of the larger. The cusps of the bicuspid valve are furnished with chordae tendineae, which are attached in a manner similar to those on the right side ; they are, however, thicker, stronger, and less numerous. [source]
The trabecule carnese are of three kinds, like those upon the right side, but they are more numerous, and present a dense interlacement, especially at the apex, and upon the posterior wall of the ventricle. The musculi papillares are two in number, one being connected to the anterior, the other to the posterior wall; they are of large size, and end in rounded extremities from which the chordae tendinese arise. The chordae tendinese from each papillary muscle are connected to both cusps of the bicuspid valve. [source]
The fibrous rings sm-roimding the arterial orifices serve for the attachment of the great vessels and semUtmar valves. Each ring receives, by its ventricular margin, the attachment of some of the muscular fibers of the ventricles; its opposite margin presents three deep semicircular notches, to which the middle coat of the artery is firmly fixed. The attachment of the artery to its fibrous ring is strengthened by the external coat and serous membrane externalh', and by the endocardium internalh'. From the margins of the semicircular notches the fibrous structm^e of the ring is continued into the segments of the valves. The middle coat of the artery in this situation is thin, and the vessel is dilated to form the sinuses of the aorta and pulmonary arterj-. [source]
Component Parts. — As has already been stated (page 497), the heart is sub- divided by septa into right and left halves, and a constriction subdivides each half of the organ into two cavities, the upper cavity being called the atrium, the lower the ventricle. The heart therefore consists of four chambers, viz., right and left atria, and right and left ventricles. [source]
The division of the heart into four cavities is indicated on its surface by grooves. The atria are separated from the ventricles by the coronary sulcus (auriculo- [source]
The intervenous tubercle (tuherculum intervenosiim; tubercle of Lower) is a small projection on the posterior wall of the atrium, above the fossa ovalis. It is distinct in the hearts of quadrupeds, but in man is scarcely visible. It was supposed by Lower to direct the blood from the superior vena cava toward the atrioventricular opening. [source]
The muscular structure of the heart consists of bands of fibers, which present an exceedingly intricate interlacement. They comprise (a) the fibers of the atria, (6) the fibers of the ventricles, and (c) the atrioventricular bundle of His. [source]
The fibers of the atria are arranged in two layers — a superficial, common to both cavities, and a deep, proper to each. The superficial fibers are most distinct on the front of the atria, across the bases of which they run in a transverse direction, forming a thin and incomplete layer. Some of these fibers run into the atrial septum. The deep fibers consist of looped and annular fibers. The looped fibers pass upward over each atrium, being attached by their two extremities to the corresponding atrioventricular ring, in front and behind. The an?iular fibers surround the auriculae, and form annular bands around the terminations of the veins and around the fossa ovalis. [source]
ventricular groove); this contains the trunks of the nutrient vessels of the heart, and is deficient in front, where it is crossed by the root of the pulmonary artery. The interatrial groove, separating the two atria, is scarcely marked on the posterior surface, while anteriorly it is hidden by the pulmonary artery and aorta. The ventricles are separated by two grooves, one of which, the anterior longitudinal sulcus, is situated on the sternocostal surface of the heart, close to its left margin, the other posterior longitudinal sulcus, on the diaphragmatic surface near the right margin; these grooves extend from the base of the ventricular portion to a notch, the incisura apicis cordis, on the acute margin of the heart just to the right of the apex. [source]
(1) the sinus venosus; (2) the primitive atrium; (3) the primitive ventricle; (4) the bulbus cordis, and (5) the tnmcus arteriosus (Figs. 461, 462). The constriction between the atrium and ventricle constitutes the atrial canal, and indicates the site of the future atrioventricular valves. [source]
Purkinje Fibers (Fig. 500). — Between the endocardiimi and the ordinary cardiac muscle are fomid, imbedded in a small amount of connective tissue, peculiar fibers known as Purkinje fibers. Thej- are fotind in certain mammals and in birds, and can be best seen in the sheep's heart, where [source]
The sternocostal surface (Fig. 492) is directed forward, upward, and to the left. Its lower part is convex, formed chiefly by the right ventricle, and traversed near its left margin by the anterior longitudinal sulcus. Its upper part is separated from the lower by the coronary sulcus, and is formed by the atria; it presents a deep concavity (Fig. 494), occupied by the ascending aorta and the pulmonary artery. [source]
The separation of the auricula from the sinus venarum is indicated externally by a groove, the terminal sulcus, which extends from the front of the superior vena cava to the front of the inferior vena cava, and represents the line of union of the sinus venosus of the embr\'o with the primitive atrium. On the inner wall of the atrium the separation is marked by a vertical, smooth, muscular ridge, the terminal crest. Behind the crest the internal surface of the airium is smooth, while in front of it the muscular fibers of the wall are raised into parallel ridges resembling the teeth of a comb, and hence named the musculi pectinati. [source]
The fossa ovalis is an oval depression on the septal wall of the atrium, and corre- sponds to the situation of the foramen ovale in the fetus. It is situated at the lower part of the septum, above and to the left of the orifice of the inferior vena cava. [source]
The pulmonary semilunar valves (Fig. 494) are three in number, two in front and one behind, formed by duplicatures of the lining membrane, strengthened by fibrous tissue. They are attached, by their convex margins, to the wall of the artery, at its junction with the ventricle, their free borders being directed upward into the lumen of the vessel. The free and attached margins of each are strength- [source]
The aortic semilunar valves (Figs. 494, 497) are three in number, and surround the orifice of the aorta; two are anterior (right and left) and one posterior. They are similar in structure, and in their mode of attachment, to the pulmonary semi- lunar valves, but are larger, thicker, and stronger; the lunula? are more distinct, and the noduli or corpora xVrantii thicker and more prominent. Opposite the valves the aorta presents slight dilatations, the aortic sinuses (sinuses of Valsalva), which are larger than those at the origin of the pulmonary artery. [source]
Structure. — The heart consists of muscular fibers, and of fibrous rings which serve for their attachment. It is covered by the visceral layer of the serous pericardium (epicardium), and lined by the endocardium. Between these two membranes is the muscular wall or myocardium. [source]
originates near the orifice of the coronary sinus, undergoes slight enlargement to form a node, passes forward to the ventricular septum, and divides into two limbs. The ultimate distribution cannot be completely shown in this diagram. [source] — course of the atrioventricular bundle
The human heart is divided by septa into right and left halves, and each half is further divided into two cavities, an upper termed the atrium and a lower the ventricle. The heart therefore consists of four chambers, two, the right atrium and right ventricle, forming the right half, and two, the left atrium and left ventricle the left half. The right half of the heart contains venous or impure blood; the left, arterial or pure blood. The atria are receiving chambers, and the ventricles dis- tributing ones. From the cavity of the left ventricle the pure blood is carried into a large artery, the aorta, through the numerous branches of which it is distributed to all parts of the body, with the exception of the lungs. In its passage through the capillaries of the body the blood gives up to the tissues the materials necessary for their growth and nourishment, and at the same time receives from the tissues the waste products resulting from their metabolism. In doing so it is changed from arterial into venous blood, which is collected by the veins and through them returned to the right atrium of the heart. From this cavity the impure blood passes into the right ventricle, and is thence conveyed through the pulmonary arteries to the lungs. In the capillaries of the lungs it again becomes arterialized, and is then carried to the left atrium by the pulmonary veins. From the left atrium it passes into the left ventricle, from which the cycle once more begins. [source]
The Ligament of the Left Vena Cava. — Between the left pulmonarj' artery and subjacent pulmonary vein is a triangular fokl of the serous pericardium; it is known as the ligament of the left vena cava (vestigial fold of Marshall). It is formed by the dupUcature of the serous layer over the remnant of the lower part of the left superior vena cava (duct of Cuvier), which becomes obhterated diu-ing fetal life, and remains as a fibrous band stretching from the highest left inter- costal vein to the left atrium, where it is continuous with a small vein, the vein of the left atrium (oblique vein of Marshall), which opens into the coronary sinus. [source]
The foramina venarum minimarum (Joramina. Thehesii) are the orifices of minute veins {ven(p cordis minima'), which return blood directly from the muscular sub- stance of the heart. [source]
The diaphragmatic surface (Fig. 491), directed downward and slightly backward, is formed by the ventricles, and rests upon the central tendon and a small part of the left muscular portion of the diaphragm. It is separated from the base by the posterior part of the coronary sulcus, and is traversed obliquely by the posterior longitudinal sulcus. [source]
The superior vena cava returns the blood from the upper half of the body, and opens into the upper and back part of the atrium, the direction of its orifice being downward and forward. Its opening has no valve. [source]
ened by tendinous fibers, and the former presents, at its middle, a thickened nodule (corpus Amntii). From this nodule tendinous fibers radiate through the segment to its attached margin, but are absent from two narrow crescentic portions, the lunulas, placed one on either side of the nodule immediately adjoining the free margin. Between the semilunar valves and the wall of the pulmonary artery are three pouches or sinuses {sinuses uf Valsalva). [source]
The pulmonary veins, four in number, open into the upper part of the posterior surface of the left atrium — two on either side of its middle line: they are not provided with valves. The two left veins frequently end by a common opening. [source]
Left Ventricle {ventriculus sinister). — The left ventricle is longer and more conical in shape than the right, and on transverse section its concavity presents an oval or nearly circular outline. It forms a small part of the sternocostal surface and a considerable part of the diaphragmatic surface of the heart; it also forms the apex of the heart. Its walls are about three times as thick as those of the right ventricle. [source]
The nerves are derived from the cardiac plexus, which are formed partly from the vagi, and partly from the sympathetic trunks. They are freely distributed both on the surface and in the substance of the heart, the separate nerve filaments being furnished with small ganglia. [source]
The right margin of the heart is long, and is formed by the right atrium above and the right ventricle below. The atrial portion is rounded and almost vertical; it is situated behind the third, fourth, and fifth right costal cartilages about [source]
The left or obtuse margin is shorter, full, and rounded: it is formed mainly by the left ventricle, but to a slight extent, above, by the left atrium. It extends from a point in the second left intercostal space, about 2.5 mm. from the sternal margin, obliquely downward, with a convexity to the left, to the apex of the heart. [source]
The Apex (apex cordis). — The apex is directed downward, forward, and to the left, and is overlapped by the left lung and pleura: it lies behind the fifth left intercostal space, 8 to 9 cm. from the mid-sternal line, or about 4 cm. below and 2 mm. to the medial side of the left mammary papilla. [source]
Cardiac Muscular Tissue. — The fibers of the heart difYer very remarkably from those of other striped muscles. They are smaller by one-third, and their transverse strite are by no means so well-marked. They show faint longitudinal striation. The fibers are made up of distinct quad- rangular cells, joined end to end so as to form a syncytium (Fig. 499). Each cell contains a clear oval nucleus, situated near its center. The extremities of the cells have a tendency to branch or di\-ide, the subdivisions miiting with offsets from other cells, and thus producing an anastomosis of the fibers. The connective tissue between the bimdles of fibers is much less than in ordinary striped muscle, and no sarcolemma has been proved to exist. [source]
Right Atrium {atrium dextrum; right auricle). — The right atrium is larger than the left, but its walls are somewhat thinner, measuring about 2 mm.; its cavity is capable of containing about 57c.c. It consists of two parts: a principal cavity, or sinus venarum, situated posteriorly, and an anterior, smaller portion, the auricula. [source]
Sinus Venarum {sinus venosus). — The sinus venarum is the large quadrangular cavity placed between the two vense cavse. Its walls, which are extremely thin, [source]
Left Atrium {atrium sinistum; left auricle) .—The left atrium is rather smaller than the right, but its walls are thicker, measuring about 3 mm.; it consists, like the right, of two parts, a principal cavity and an auricula. [source]
ance to the inner surface of the heart; it assists in forming the valves b\' its reduplications, and is continuous with the Uning membrane of the large bloodvessels. It consists of connective tissue and elastic fibers, and is attached to the muscular structure by loose elastic tissue which contains bloodvessels and nerves; its free surface is covered by endothehal cells. [source]
1.25 cm. from the margin of the sternum. The ventricular portion, thin and sharp, is named the acute margin; it is nearly horizontal, and extends from the sternal end of the sixth right costal cartilage to the apex of the heart. [source]
Vessels and Nerves. — The arteries supplying the heart are the right and left coronary from the aorta; the veins end in the right atrium. [source]
The heart and lungs are situated in the thorax, the walls of which afford them protection. The heart lies between the two lungs, and is enclosed within a fibrous bag, the pericardium, while each lung is invested by a serous membrane, the pleura. The skeleton of the thorax, and the shape and boundaries of the cavity, have already been described (page 117). [source]
The base {basis cordis) (Fig. 491), directed upward, backward, and to the right, [source]
separated from the left ventricle, but remains an integral part of the right ventricle, of which it forms the infundibulum (Fig. 469). [source]
flattened cells resting on loose connective tissue. The heart invaginates the wall of the serous sac from above and behind, and practically obliterates its cavity, the space being merely a potential one. [source]
^ esophagus, aorta, and thoracic duct. It is formed mainly by the left atrium, [source]
Auricula (auricula dextra; right auricular appendix). — The auricula is a small conical muscular pouch, the margins of which present a dentated edge. It projects from the upper and front part of the sinus forward and toward the left side, over- lapping the root of the aorta. [source]
In front, it is separated from the anterior wall of the thorax, in the greater part of its extent, by the lungs and pleiirse ; but a small area, somewhat variable in size, and usually corresponding with the left half of the lower portion of the body of the sternum and the medial ends of the cartilages of the fourth and fifth ribs of the left side, comes into direct relationship with the chest wall. The lower extrem- ity of the thymus, in the child, is in contact with the front of the upper part of the pericardium. Behind, it rests upon the bronchi, the esophagus, the descending thoracic aorta, and the posterior part of the mediastinal surface of each lung. Laterally, it is covered by the pleurae, and is in relation with the mediastinal sur- faces of the lungs; the phrenic nerve, with its accompanying vessels, descends between the pericardium and pleura on either side. [source]
The fibrous pericardium forms a flask-shaped bag, the neck of which is closed by its fusion with the external coats of the great vessels, while its base is attached to the central tendon and to the muscular fibers of the left side of the diaphragm. In some of the lower mammals the base is either completely separated from the diaphragm or joined to it by some loose areolar tissue; in man much of its diaphragmatic attachment consists of loose fibrous tissue which can be readily broken downi, but over a small area the central tendon of the diaphragm and the pericardium are completely fused. Above, the fibrous pericardium not only blends with the external coats of the great vessels, but is continuous with the pretracheal laxev of the deep cervical fascia. By means of these upper and lower connections it is securely anchored within the thoracic cavity. It is also attached to the posterior surface of the sternum by the superior and inferior stemopericardiac ligaments; the upper passing to the manubrium, and the lower to the xiphoid process. [source]
The vessels receiving fibrous prolongations from this membrane are: the aorta, the superior vena cava, the right and left pulmonar}^ arteries, and the four pulmonary veins. The inferior vena cava enters the pericardium through the central tendon of the diaphragm, and receives no covering from the fibrous layer. [source]

How it works

lowed, after a slight pause, by (2) a simultaneous, but more prolonged, contraction of both ventricles, named the ventricular systole, and (3) a period of rest, during which the whole heart is relaxed. The atrial contraction commences around the venous openings, and sweeping over the atria forces their contents through the atrio- ventricular openings into the ventricles, regurgitation into the veins being pre- vented by the contraction of their muscular coats. When the ventricles contract, the tricuspid and bicuspid valves are closed, and prevent the passage of the blood back into the atria; the musculi papillares at the same time are shortened, and, pulling on the chorda^ tendincfe, prevent the inversion of the valves into the atria. As soon as the pressure in the ventricles exceeds that in the pulmonary artery and aorta, the valves guarding the orifices of these vessels are opened and the blood is driven from the right ventricle into the pulmonary artery and from the left into the aorta. The moment the systole of the ventricles ceases, the pressure of the blood in the pulmonary artery and aorta closes the pulmonary and aortic semilunar valves to prevent regurgitation of blood into the ventricles, the valves remaining shut until reopened by the next ventricular systole. During the period of rest the tension of the tricuspid and bicuspid valves is relaxed, and blood is flowing from the veins into the atria, being aspirated by negative intrathoracic pressure, and slightly also from the atria into the ventricles. The average duration of a cardiac cycle is about yt of a second, made up as follows : [source]
The truncus arteriosus and bulbus cordis are divided by the aortic septum (Fig. 470). This makes its appearance in three portions. (1) Two distal ridge-Hke thickenings project into the lumen of the tube; these increase in size, and ultimately meet and fuse to form a septum, which takes a spiral course toward the proximal end of the truncus arteriosus. It divides the distal part of the truncus into two vessels, the aorta and pulmonary artery, which lie side by side above, but near the heart the pulmonary artery is in front of the aorta. (2) Four endocardial cushions appear in the proximal part of the truncus arteriosus in the region of the future semilunar valves; the manner in which these are related to the aortic septum is described below. (3) Two endocardial thickenings — anterior and posterior — [source]
The primitive atrium grows rapidly and partially encircles the bulbus cordis; the groove against which the bulbus cordis lies is the first indication of a division into right and left atria. The cavity of the primitive atrium becomes subdivided into right and left chambers by a septum, the septum primum (Fig. 4()5), which grows downward into the ca"\'ity. For a time the atria communicate with each other by an opening, the ostium primum of Born, below the free margin of the septum. This opening is closed by the union of the septum primum with the septum inter- medium, and the communication between the atria is reestablished through an opening which is developed in the upper part of the septum primum; this opening is known as the foramen ovale {ostium secundum of Born) and persists imtil birth. [source]
septum, the sinus septum, grows from the posterior wall of the sinus venosus to fuse with the valve and divide it into two parts — an upper, the valve of the inferior vena cava, and a lower, the valve of the coronary sinus (Fig. 4()S). The extreme upper portion of the right venous valve, together with the septum spurium, form [source]
In the inferior vena cava, the blood carried by the ductus venosus and hepatic veins becomes mixed with that returning from the lower extremities and abdominal wall. It enters the right atrium, and, guided by the valve of the inferior vena cava, passes through the foramen ovale into the left atrium, where it mixes with a small quantity of blood returned from the lungs by the pulmonary veins. From the left atrium it passes into the left ventricle; and from the left ventricle into the aorta, by means of which it is distributed almost entirely to the head and upper extremities, a small quantity being probably carried into the descending aorta. From the head and upper extremities the blood is returned by the superior vena cava to the right atrium, where it mixes with a small portion of the blood from the inferior vena cava. P'rom the right atrium it descends into the right ventricle, and thence passes into the pulmonary artery. The lungs of the fetus being inactive, only a small quantity of the blood of the pulmonary artery is distributed to them by the right and left pulmonary arteries, and returned by the pulmonary veins to the left atrium : the greater part passes through the ductus arteriosus into the aorta, where it mixes with a small quantity of the blood transmitted by the left ventricle into the aorta. Through this vessel it descends, and is in part distributed [source]
communicates freely with the right ventricle, while the junction of the bulbus with the truncus arteriosus is brought directly ventral to and applied to the atrial canal. By the upgrowth of the ventricular septum the bulbus cordis is in great measure [source]
The Valves of the Heart. — The atrioventricular valves are developed in relation to the atrial canal. By the upward expansion of the bases of the ventricles the canal becomes invaginated into the ventricular cavities. The invaginated margin forms the rudiments of the lateral cusps of the atrioventricular valves; the mesial or [source]
The Cardiac Cycle and the Actions of the Valves. — By the contractions of the heart the blood is pumped through the arteries to all parts of the body. These contractions occur regularly and at the rate of about seventy per minute. Each wave of contraction or period of activity is followed by a period of rest, the two periods constituting what is known as a cardiac cycle. [source]
Each cardiac cycle consists of three phases, which succeed each other as follows: (1) a short simultaneous contraction of both atria, termed the atrial systole, fol- [source]
the crista terminalis already mentioned. The upper and middle thirds of the left venous valve disappear; the lower third is continued into the spina vestibuli, and later fuses with the septum secundum of the atria and takes part in the forma- tion of the limbus fossae ovalis. [source]
septal cusps of the valves are developed as downward prolongations of the septum intermedium (Fig. 467). The aortic and pulmonary semilunar valves are formed from four endocardial thickenings — an anterior, a posterior, and two lateral — which appear at the proximal end of the truncus arteriosus. As the aortic septum grows downward it divides each of the lateral thickenings into two, thus giving rise to six thickenings — the rudiments of the semilunar valves — three at the aortic and three at the pulmonary orifice (Fig. 471). [source]
Clinical and experimental evidence go to prove that this bundle conveys the impulse to sys- tolic contraction from the atrial septum to the ventricles. [source]
The rhythmical action of the heart is muscular in origin^ — that is to say, the heart muscle itself possesses the inherent property of contraction apart from any nervous stimulation. The more embryonic the muscle the better is it able to initiate and propagate the contraction wave; this explains why the normal systole of the heart starts at the entrance of the veins, for there the muscle is most embryonic in nature. At the atrioventricular junction there is a slight pause in the wave of muscular contraction. To obviate this so far as possible a peculiar band of marked embryonic type passes across the junction and so carries on the contraction wave to the vpntricles. This band, composed of special fibers, is the atrioventricular bundle of His (p. 537). The nerves, although not concerned in originating the contractions of the heart muscle, play an important role in regulating their force and frequency in order to subserve the physiological needs of the organism. [source]
When the heart assumes its S-shaped form the bulbus cordis lies ventral to and in front of the primitive ventricle. The adjacent walls of the bulbus cordis and ventricle approximate, fuse, and finally disappear, and the bulbus cordis now [source]
The atrial canal is at first a short straight tube connecting the atrial with the ventricular portion of the heart, but its growth is relatively slow, and it becomes overlapped by the atria and ventricles so that its position on the surface of the heart is indicated onlv bv an annular constriction (Fig. 406). Its lumen is reduced to a [source]
develop in the bulbus cordis and unite to form a short septum; this joins above with the aortic septum and below with the ventricular septum. The septum grows down into the ventricle as an oblique partition, which ultimately blends with the ven- tricular septum in such a way as to bring the bulbus cordis into communication with the pulmonary artery, and through the latter with the sixth pair of aortic arches; while the left ventricle is brought into continuity with the aorta, which communicates with the remaining aortic arches. [source]
Soon, however, it assumes an oblique position, and becomes crescentic in form; its right half or horn increases more rapidly than the left, and the opening into the atrium now communicates with the right portion of the atrial cavity. The right horn and transverse portion of the sinus ultimately become incorporated with and form a part of the adult right atrium, the line of union between it and the auricula being indicated in the interior of the atrium by a vertical crest, the crista terminalis of His. The left horn, which- ultimately receives onh' the left duct of Cuvier, [source]
persists as the coronary sinus (Fig. 4(34) . The vitelline and umbilical veins are soon replaced by a single vessel, the inferior vena cava, and the three veins (inferior vena cava and right and left Cuvierian ducts) open into the dorsal aspect of the atrium by a common slit-like aperture (Fig. 465). The upper part of this aperture repre- sents the opening of the permanent superior vena cava, the lower that of the inferior vena cava, and the intermediate part the orifice of the coronary sinus. The slit- [source]
The valve of the inferior vena cava serves to direct the blood from that vessel through the foramen ovale into the left atrium. [source]
vena cava being guided by the valve of this vessel into the left atrium, while that in the superior vena cava descends into the right ventricle. At an early period of fetal life it is highly probable that the two streams are quite distinct; for the inferior vena cava opens almost directly into the left atrium, and the valve of the inferior vena cava would exclude the current from the right ventricle. At a later period, as the separation between the two atria becomes more distinct, it seems probable that some mixture of the two streams must take place. (4) The pure blood carried from the placenta to the fetus by the umbilical vein, mixed with the blood from the portal vein and inferior vena cava, passes almost directly to the arch of the aorta, and is distributed by the branches of that vessel to the head and upper extremities. (5) The blood contained in the descending aorta, chiefly derived from that which has already circulated through the head and limbs, together with a small quantity from the left ventricle, is distributed to the abdomen and lower extremities. [source]
anterior wall of the umbilical orifice are now continuous with the posterior ends of the anterior ventral aorta. With the formation of the tail-fold the posterior parts of the primitive aortje are carried forward in a ventral direction to form the pos- terior ventral aortie and primary caudal arches.^ In the pericardial region the two primitive aortre grow together, and fuse to form a single tubular heart (Fig. 460), the posterior end of which receives the two vitelline veins, while from its anterior end the two anterior ventral aortae emerge.^ The first cephalic arches pass through the mandibular arches, and behind them five additional pairs subsequently develop, so that altogether six pairs of aortic arches are formed; the fifth arches are very transitory vessels connecting the ventral aortse with the dorsal ends of the sixth arches. By the rhythmical contraction of the tubular heart the blood is forced through the aortae and bloodvessels of the vascular area, from which it is returned to the heart by the vitelline veins. This constitutes the vitelline circulation (Fig. 459), and by means of it nutri- ment is absorbed from the yolk (vitellus.) [source]
Further Development of the Heart. — Between the endothelial lining and the outer wall of the heart there exists for a time an intricate trabecular network of mesodermal tissue from which, at a later stage, the musculi papillares, chordae tendinea^, and trabecular carneue are developed. The simple tubular heart, already [source]
The sinus venosus is at first situated in the septum transversum (a layer of mesoderm in which the Uver and the central tendon of the diaphragm are devel- oped) behind the primitive atrium, and is formed by the union of the vitelline veins. The veins or ducts of Cuvier from the body of the embryo and the umbilical veins from the placenta subsequently open into it (Fig. 463). The sinus is at first place transversely, and opens by a median aperture into the primitive atrium. [source]
transverse slit, and two thickenings appear, one on its dorsal and another on its ventral wall. These thickenings, or endocardial cushions (Fig. 405) as they are termed, project into the canal, and, meeting in the middle line, unite to form the septum intermedium which divides the canal into two channels, the future right and left atrioventricular orifices. [source]
The foramen ovale, situated at the lower part of the atrial septum, forms a free communication between the atria until the end of fetal life. A septum (septum secundum) grows down from the upper wall of the atrium to the right of the primary [source]
Eternod- describes the circulation in an embryo which he estimated to be about thirteen days old (Fig. 458). The rudiment of the heart is situated immediately below the fore-gut and consists of a short stem. It gives off two vessels, the primi- tive aortae, which run backward, one on either side of the notochord, and then pass into the body-stalk along which they are carried to the chorion. From the chorionic villi the blood is returned by a pair of umbilical veins which unite in the body-stalk to form a single vessel and subsequently encircle the mouth of the yolk-sac and open into the heart. At the junction of the yolk-sac and body-stalk each vein is joined by a branch from the vascular plexus of the yolk-sac. From his observations it seems that, in the human embryo, the chorionic circulation is established before that on the yolk-sac. [source]
fold named the septum spurium; below the opening they fuse to form a triangular thickening — the spina vestibuli. The right venous valve is retained; a small [source]
exists above its ventral portion (Fig. 468), but this foramen is ultimately closed by the fusion of the aortic septum with the ventricular septum. [source]
septum in which the foramen ovale is situated; shortly after birth it fuses with the primary septum and the foramen ovale is obliterated. [source]
The course of the blood from the left ventricle through the body generally to the right side of the heart constitutes the greater or systemic circulation, while its passage from the right ventricle through the lungs to the left side of the heart is termed the lesser or pulmonary circulation. [source]
The heart originally lies on the ventral aspect of the pharynx, immediately behind the stomodeum. With the elongation of the neck and the development of the lungs it recedes within the thorax, and, as a consequence, the anterior ventral aortse are drawn out and the original position of the fourth and fifth arches' is greatly modified. Thus, on the right side the fourth recedes to the root of the neck, while on the left side it is withdrawn within the thorax. The recurrent nerves originally pass to the larynx under the sixth pair of arches, and are there- fore pulled backward with the descent of these structures, so that in the adult the left nerve hooks around the ligamentum arteriosum; owing to the disappearance of the fifth and the sixth right arches the right nerve hooks around that immediately above them, i. c, the commencement of the subclavian artery. Segmental arteries arise from the primitive dorsal aortse and course between successive segments. The seventh segmental artery is of special interest, since it forms the lower end of the vertebral artery and, when the forelimb bud appears, sends a branch to it (the subclavian artery). From the seventh segmental arteries the entire left subclavian and the greater part of the right subclavian are formed. The second pair of segmental arteries accompany the hypoglossal nerves to the brain and are named the hypoglossal arteries. Each sends forward a branch which forms the cerebral part of the vertebral artery and anastomoses with the posterior branch of the internal carotid. The two vertebrals unite on the ventral surface of the hind-brain to form the basilar artery. Later the hypoglossal artery atrophies and the vertebral is connected with the first segmental artery. The cervical part of the vertebral is developed from a longitudinal anastomosis between the first seven segmental arteries, so that the seventh of these ultimately becomes the source of the artery. As a result of the growth of the upper limb the subclavian artery increases greatly in size and the vertebral then appears to spring from it. [source]
Changes in the Vascular System at Birth. — At birth, when respiration is estab- lished, an increased amount of blood from the pulmonary artery passes through the lungs, and the placental circulation is cut off. The foramen ovale is closed by about the tenth day after birth: the valvular fold above mentioned adheres to the margin of the foramen for the greater part of its circumference, but a slit-like opening is left between the two atria above, and this sometimes persists. [source]
The first rudiment of the heart appears as a pair of tubular vessels which are developed in the splanchnopleure of the peri- cardial area (Fig. 457). These are named the primitive aortae, and a direct continuity is soon established between them and the vessels of the yolk-sac. Each receives anteriorly a vein— the vitelline vein — from the yolk-sac, and is prolonged backward on the lateral aspect of the noto- chord under the name of the dorsal aorta. The dorsal aortse give branches to the yolk-sac, and are continued backward tlu-ough the body-stalk as the umbilical arteries to the villi of the chorion. [source]
By the forward growth and flexure of the head the pericardial area and the anterior portions of the primitive aortse are folded backward on the ventral aspect of the fore-gut, and the original relation of the somatopleure and splanchnopleure layers of the pericardial area is reversed. Each primitive aorta now consists of a ventral and a dorsal part connected anteriorly by an arch (Fig. 459) ; these three parts are named respectively the anterior ventral aorta, the dorsal aorta, and the first cephalic arch. The vitelline veins which enter the embryo through the [source]
The ductus arteriosus begins to contract immediately after respiration is estab- lished, and is completely closed from the fourth to the tenth day; it ultimately degenerates into an impervious cord, the ligamentum arteriosum, which connects the left pulmonary artery to the arch of the aorta. [source] — fetal shunt closing after birth

Measurements and reference values

Atrial systole, yV- Atrial diastole, yV. [source] — phase durations; the fractions are garbled by OCR
Ventricular systole, ^. Ventricular diastole, y-g-. [source] — phase durations; the fractions are garbled by OCR
Total systole, yy. Complete diastole, -y^- [source] — phase durations; the fractions are garbled by OCR
Size. — The heart, in the adult, measures about 12 cm. in length, 8 to 9 cm. in breadth at the broadest part, and 6 cm. in thickness. Its weight, in the male, varies from 280 to 340 grams; in the female, from 230 to 280 grams. The heart continues to increase in weight and size up to an advanced period of life; this increase is more marked in men than in women. [source]

Problems, failure modes and limitations

A second septum, the septum secimdum (Figs. 467, 468), semilunar in shape, grows downward from the upper wall of the atrium immediately to the right of the primary septum and foramen ovale. Shortly after birth it fuses with the primary septum, and by this means tiie foramen ovale is closed, but sometimes the fusion is incomplete and the upper part of the foramen remains patent. The limbus fossse ovalis denotes the free margin of the septum secundum. Issuing from each lung is a pair of pulmonary veins; each pair unites to form a single vessel, and these in turn join in a common trunk which opens into the left atrium. Subsequently the common trunk and the two vessels forming it expand and form the vestibule or greater part of the atrium, the expansion reaching as far as the openings of the four vessels, so that in the adult all four veins open separately into the left atrium. The primitive ventricle becomes divided by a septum, the septmn inferius or ventricular septmn (Figs. 465, 466, 467), which grows upward from the lower part of the ventricle, its position being indicated on the surface of the heart by a furrow. Its dorsal part increases more rapidly than its ventral portion, and fuses Avith the dorsal part of the septum intermedium. For a time an interventricular foramen [source] — septum secundum; the foramen ovale may remain patent
Ventricular Septum [septum ventriculorum; interventricular septum) (Fig. 498). — The ventricular septum is directed obliquely backward and to the right, and is curved with the convexity toward the right ventricle: its margins correspond with the anterior and posterior longitudinal sulci. The greater portion of it is thick and muscular and constitutes the muscular ventricular septum, but its upper and posterior part, which separates the aortic vestibule from the lower part of the right atrium and upper part of the right ventricle, is thin and fibrous, and is termed the membranous ventricular septum. An abnormal communication may exist between the ventricles at this part owing to defective development of the membranous septum. [source] — ventricular septum; defect of its membranous part

Comparisons and alternatives

The chief peculiarities of the fetal heart are the direct communication between the atria through the foramen ovale, and the large size of the valve of the inferior vena cava. Among other peculiarities the following may be noted. (1) In early fetal life the heart lies immediately below the mandibular arch and is relatively large in size. As development proceeds it is gradually dra^^^l within the thorax, but at first it lies in the middle line ; toward the end of pregnancy it gradually becomes oblique in direction. (2) For a time the atrial portion exceeds the ventricular in size, and the w^alls of the ventricles are of equal thickness : toward the end of fetal life the ventricular portion becomes the larger and the wall of the left ventricle exceeds that of the right in thickness. (3) Its size is large as compared with that of the rest of the body, the proportion at the second month being 1 to 50, and at birth, 1 to 120, while in the adult the average is about 1 to 160. [source] — fetal heart versus adult
2 In most fishes and in the amphibia the heart originates as a single median tube. [source] — comparative: fishes and amphibia

Facts and statements

The opening of the pulmonary artery is circular in form, and situated at the summit of the conus arteriosus, close to the ventricular septum. It is placed above and to the left of the atrioventricular opening, and is guarded by the pulmonary semilunar valves. [source]
The valve of the coronary sinus {valvula sinus coronarii [Thebesii]; Thebesian valve) is a semicircular fold of the lining membrane of the atrium, at the orifice of the coronary sinus. It prevents the regurgitation of blood into the sinus during the contraction of the atrium. This valve mav be double or it mav be cribriform. [source]
The left atrioventricular opening {mitral orifice) is placed below and to the left of the aortic orifice. It is a little smaller than the corresponding aperture of the opposite side, admitting only two fingers. It is surrounded by a dense fibrous ring, covered by the lining membrane of the heart, and is guarded by the bicuspid or ipitral valve. [source]
On the atrial septum may be seen a lunated impression, bounded below by a crescentic ridge, the concavity of which is turned upward. The depression is just above the fossa ovalis of the right atrium. [source]
The principal cavity is cuboidal in form, and concealed, in front, by the pul- monary artery and aorta; in front and to the right it is separated from the right atrium by the atrial septum; opening into it on either side are the two pulmonary [source]
Dr. A. Morison^ has shown that in the sheep and pig the atrioventricular bundle "is a great avenue for the transmission of nerves from the auricular to the ventricular heart; large and numerous nerve trunks entering the bundle and coursing with it." From these, branches pass off and form plexuses around groups of Purkinje cells, and from these plexuses fine fibrils go to innervate individual cells. [source]
Auricula {auricula sinistra; left auricular appendix).— The auricula is somewhat constricted at its junction with the principal cavity ; it is longer, narrower, and more curved than that of the right side, and its margins are more deeply indented. It is directed forward and toward the right and overlaps the root of the pulmonary artery. [source]
The musculi pectinati, fewer and smaller than in the right auricula, are confined to the inner surface of the auricula. [source]
The nerves of the percardium are derived from the vagus and phrenic nerves, and the sj'mpa- thetic trunks, [source]
rpHE vascular system is divided for descriptive purposes into (a) the blood J- vascular system, which comprises the heart and bloodvessels for the circula- tion of the blood; and (6) the lymph vascular system, consisting of lymph glands and lymphatic vessels, through which a colorless fluid, the lymph, circulates. It must be noted, however, that the two systems communicate with each other and are intimately associated developmentally. [source]
The arteries of the pericardium are derived from the internal mammary and its musculo- phrenic branch, and from the descending thoracic aorta. [source]

Related concepts

atrium — is a part of Heart
ventricle — is a part of Heart
coronary artery — is a part of Heart
blood vascular system — is a whole of Heart
papillary muscle — is a part of Heart
valve — is a part of Heart; the heart's valves; venous valves are excluded
septum — is a part of Heart
sinus venosus — is a part of Heart; the embryonic heart and its derivatives
cardiac — is a synonym of Heart
atrioventricular opening — is a part of Heart
pericardium — is a part of Heart
foramen ovale — is a part of Heart
crista terminalis — is a part of Heart
apex of the heart — is a part of Heart
semilunar valve — is a part of Heart
myocardium — is a part of Heart
conus arteriosus — is a part of Heart
atrioventricular bundle — is a part of Heart
coronary sinus — is a part of Heart
tricuspid valve — is a part of Heart

Children

No children recorded.

← the whole tree · 3D view· how to read this page