504 SANGUIFEROUS SYSTEM. 



its position, extending along the middle of the sternum, and 

 more longitudinal in its direction, with the apex at a variable 

 distance from the diaphragm, than in the higher quadrupeds 

 and man, where it is directed more transversely, inclines to 

 the ribs of the left side with its apex, and rests with its 

 pericardium contiguous to the diaphragm. The right ven- 

 tricle being shorter and broader than the left, the superficial 

 groove of separation between them lies to the right side of 

 the apex, and marks the direction of the coronary arteries, 

 which arise from the commencement of the aorta; the 

 coronary veins terminate by a valved orifice directly in the 

 right auricle, which generally presents a distinct muscular 

 auricular appendix, a permanent fossa ovalis, and a remnant, 

 more or less distinct, of the Eustachian valve so important 

 in the foetus. The nerves of the heart are derived from the 

 great sympathetic and the pneumogastric, as in other classes. 

 The entire heart is more oblique in its position, with its 

 posterior surface more approximated to the diaphragm, and 

 the pericardium is more intimately connected by cellular sub- 

 stance to the middle tendinous part of that muscle, in man 

 and the higher quadrumana, than in the inferior quadrupeds 

 where the lower vena cava is consequently longer. It is also 

 sinistral in its direction in the mole, from the size of the right 

 lung. It is also in man and the quadrumana that we find 

 the Eustachian valve most developed, and in several rodentia. 

 The muscular parietes of the right ventricle appear propor- 

 tionately thicker in the porpoise and other cetacea, than in 

 terrestrial quadrupeds. In the right ventricle of the ornitho- 

 rhynchus, the tricuspid valve is muscular, like that of a bird. 

 The semilunar valves, at the origins of the aorta and pulmo- 

 nary artery, are three in number, as in birds, and are provided 

 with the same prominent corpuscula Aurantii in the middle 

 of their free margin, and here also the coronary arteries, to 

 supply the heart, commence in the fosse behind these valves. 

 In the heart of many of the adult ruminating and pachyder- 

 matous quadrupeds, one or two considerable cruciform 

 osseous laminae are almost constantly found at the base of 

 the septum ventriculorum, between the origins of the great 

 arteries from the ventricles, as seen also in the adult saurian 

 and chelonian reptiles. 



In the mammalia as in birds, there are most generally 



