either the postcaval or coronary veins: the contrast presented by the Elephant, in this respect, is significant. The strong chorda tendineæ of the tricuspid connect it, in most Ungulates, with three obtuse and transversely oblong carneæ columnæ: one rising from the movable wall, a second from the septum, and a third smaller one from the anterior interspace between the fixed and movable walls: the tendons diverge from each column to the two contiguous moieties of the divisions of the tricuspid—a provision ensuring the simultaneous action and outstretching of the three portions of the valve. Two smaller columns placed opposite to each other, one on the free, the other on the fixed wall, are connected in the Rhinoceros and many other Ungulates, by a single strong tendon passing across the cavity from the apex of one to the other.' In the Hog some of the tricuspid tendons pass to a thick short column' projecting from the free wall, others pass directly into the smooth convex fixed wall of the ventricle.

6

In most Ruminants, especially the larger kinds, there is a bent bone at the base of the heart, on the septal side of the origin of the aorta, and imbedded in the tendinous circle which gives attachment to muscular fibres of the ventricle; in the Giraffe this bone was two-thirds of an inch in length. Two such ossifications of the sclerous tissue have here been met with in Oxen and Red-deer: an ossified and an unossified piece of fibro-cartilage are more commonly observed: in the Horse these bodies at the septal side of the aortic ring are rarely ossified until extreme age.

F. Heart of Carnivora.-In the present group the heart is more obtuse at the apex, and the left ventricle forms a greater share thereof, than in Ungulates. The Eustachian valve is wanting in most Carnivora; where indicated, its remains have been found in the smaller kinds, as the Weasel, Polecat, Ichneumon, which by their size resemble the immature of the larger species. The inner surface of the ventricles, especially the right, is more fasciculated, and the number of carnea columnæ is greater than in Ruminants. A condensation of the sclerous tissue of the aortic ring in the Lion and Tiger, at two points, indicates the homologues of the heart-bones in Ungulates. In these and other Felines the mammillary columns are continued from the septal end of a strong trabecular tract between the 'fixed' and 'free' walls of the right ventricle. The heart in Phocide is broad and somewhat flattened,

I have not found, in Ruminants, so exclusive an origin of the mammillary columns from the 'free' or external wall, as described in ccxxxix. t. III. p. 502, after CLXXXV".

6

with an obtuse apex: the appendix of the right auricle is bifid, one process covering the origin of the pulmonary artery, the other lying upon the right ventricle. The auricular septum seems to be formed by an extension of the left part of the wall of the anterior cava, terminating in an arch to the right of the postcaval orifice, which thus seems to open (as it did in the embryo) into the left auricle. In the younger of two Seals, (Phoca vitulina), which I dissected,' the valve that cuts off this original communication between the auricles was incomplete, and left a large foramen ovale:' in the older Seal, not full grown, the valvula foraminis ovalis' was complete as to its extent, and the margins were adherent, save at the upper part where an oblique aperture, admitting a goose-quill, remained. In a young Walrus, the entire margin of the valve was adherent, and there was no intercommunication between the right and left sides of the heart. A broad crescentic fold, looking downward, divides the sinus, or fossa, receiving the precaval vein from the larger and deeper one receiving the postcaval one: this fold answers to the upper border of the 'fossa ovalis 'in the human heart; there is no orifice in the 'fossa' communicating with the left auricle. There is a small semilunar valve at the coronary orifice, but no Eustachian valve. The appendix of the auricle, in Trichechus, extends in front of the base of the aorta as far as the pulmonary artery, gradually contracting to an obtuse point: in Cystophora proboscidea the auricular appendix is short, broad, and bifid; in both it is occupied by a reticular arrangement of carnea columnæ. ventricles are broader in proportion to their length, and the apex is not produced in Trichechus, as in Cystophora proboscidea: the tendinous cords of the anterior division of the tricuspid valve, and a few of those of the right or external division, are attached to a short and thick fleshy column from the free wall of the ventricle; this column is connected by a short and thick 'trabecula' with the septum: most of the other tendinous cords are attached to the septum, and a few to trabeculæ connecting that fixed wall with the free wall of the ventricle. The pulmonary artery presents no peculiarity; it is connected by the ligamentous remnant of the ' ductus arteriosus,' which is 10 lines long and 5 lines in diameter, to the under part of the aortic arch, just beyond the origin of the left subclavian; its cavity is obliterated, but a short, thick, semilunar fold of the lining membrane of the aorta, with its concavity turned toward the end of the arch, indicates the place of the former foetal communicating channel.

The

G. Heart of Quadrumana.-In the Aye-aye, as in other Lemuride, the heart is rounded, subdepressed, with a very obtuse apex; much resembling that of the four-months foetus in Man: the right auricle is much larger than the left: it receives the blood by a single precaval, by the postcaval and coronary veins. There are both Eustachian and Thebesian valves, and a wellmarked fossa and annulus ovalis. These also characterise the right auricle in higher Quadrumana. The carneæ columnæ and chorda tendineæ are more numerous in the right ventricle of Monkeys and Baboons, relatively, than in Man: the divisions of the tricuspid terminate in a broad and rounded margin; that next the orifice of the pulmonary artery being, as usual, the largest. In the left ventricle the columnæ carneæ are numerous and small, giving a strongly reticulate character to the inner surface.

The pericardium, which has a limited adhesion to the diaphragm, opposite the apex of the heart, in Lemurs, progressively becomes less perpendicular in the thorax as the Quadrumana rise in the scale, with concomitant shortness of the thoracic post-cava, and increasing extent of adhesion of the pericardium to the diaphragm: but in none is the heart so broad at the base, so flattened, or so extensively supported by the diaphragm, as in Man.

H. Heart of Bimana.-In the prone trunk of quadrupeds the pericardium adheres to the sternum, rarely to the diaphragm; in erect bipeds the connections are reversed: no Mammal has so large a proportion of the heart resting upon the diaphragm as Man, where the central aponeurosis is concomitantly expanded for the attachment of the intervening part of the pericardium. Here the heart lies obliquely, not, as in most Mammals, parallel with the mesial plane: the apex, less acute than in Ruminants, and less obtuse than in aquatic Mammals, is directed downward, forward, and to the left, notching the anterior margin of the left lung, and beating across the interval between the cartilages of the fifth and sixth left ribs. The appendix of the right auricle has one undivided apex, extending over the origin of the aorta to that of the pulmonary artery. The single precaval terminates at the upper part of the auricle on a plane anterior to that of the postcaval, which is at the lower part: from the anterior margin of this orifice is continued the valvular fold called 'Eustachian,’ which is often reduced in substance to a filmy network, or may be wanting between the postcaval orifice and that leading to the ventricle is the opening of the coronary vein, with its valve: above the Eustachian valve is the depression, fossa ovalis,' indicative of the closed oval intercommunicating vacuity in the

septum of the foetal auricles; bounded above by the prominent crescentic border, or annulus ovalis.' The opening into the ventricle is bordered by a sclerous oval ring, to which muscular fibres of both auricle and ventricle are attached; the ring being thicker for the latter.

In the Human right ventricle the portion of the tricuspid valve nearest the orifice of the pulmonary artery is the largest, and is divided by deeper notches from the two smaller portions than these are from each other: the chorda tendineæ from each columna carnea are inserted, generally into the contiguous borders of two portions of the valve: the muscular prominences of the inner surface of the ventricle have either their inner or central surfaces free, or are free in the circumference of their middle part but attached at both ends, like beams (trabecula), or they project freely in a conical form, as 'columnæ mammillares: they are least developed in the conical prolongation of the cavity, (infundibulum, conus arteriosus), from the apex of which the pulmonary artery arises. The arterial orifice of the ventricle is formed by

sclerous tissue, which a dissector may define as a ring, fig. 405, disposed in three crescentic curves, with the convexities, a, a, toward the ventricle, and the blended horns, d, b, projecting toward the artery: the ring is represented as cut through at one of these points of confluence, e, e, in order to its being spread out. Muscular fibres of the right ventricle, f, f, are attached to the convexities of the ring; the fibrous coat of the artery is attached to the outer margin, the sigmoid valves, fig. 406, a, a, to the inner margin, of the upper or arterial surface of the concavities. which owe their definition to the junction of the endocardium to such valvular attachments. The right ventricle continues to show, in Man as in other Mammals, the same relation, as an appendage to the left, which is illustrated in the section of the Bird's heart, vol. ii., fig. 92, forming, as so seen, a concave parabolic section of a cone, applied to the more perfect cone of the left

ventricle: but the walls are relatively thicker to those of the left ventricle than in Birds.

6

407

The left auricle, figs. 408 and 409, LA, lies to the left and back part of the base of the heart, is transversely oblong and subquadrate behind; its auricular appendage comes forward into view curving to the right, upon the base of the pulmonary artery. The walls of the sinus venosus' are thicker than those in the right auricle: the terminal orifices of the pulmonary veins, usually one on each side, sometimes two on the right and one on the left, are undefended by valves: on the septum, the foetal foramen is feebly indicated by a crescentic depression. The opening into the left ventricle is smaller than the right auriculoventricular one: it is defended by the pair of triangular folds of endocardium, called the bicuspid' or 'mitral' valve. Of these the largest, fig. 407, a, hangs between the auricular and aortic orifices, and is in part reflected from the sclerous ring of the latter a small fold commonly also projects at each angle of junction of the larger folds. The chief conical 'columnæ' are two in number, and larger than those of the right ventricle; their apices are shown at fig. 407, p, p, each contributing tendinous cords to the portion of the mitral valve, a. The distribution of the chorda tendineæ, from each column to contiguous borders of the two parts of the mitral, obviously illustrates the adaptation to bring those margins together in the contraction of the ventricle. The semilunar valves at the aortic orifice, ib. d, are thicker than those of the pulmonary artery, the Valsalval sinuses,' e, are deeper, and the corpora arantii' larger: the muscular walls of the left ventricle are about three times thicker than those of the right: some of the inner longitudinal fibres, ib. b, are attached to that part of the aortic ring, not preoccupied by the larger mitral fold, a. The left ventricle is longer and narrower than the right and alone forms the apex: the two large mammillary columns occupy the lower three-fourths of the cavity, rising in its axis: the fibres radiate from their base and wind round the axis, being progressively