HEART OF BIMANA. 525 



G. Heart of Quadrumana. — In the Aye -aye, as in other Le- 

 muridce, 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 well- 

 marked fossa and anuulus ovalis. These also characterise the 

 right auricle in higher Quadrumana. The carneae columnae and 

 chordae tendineae 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 columnae carneae 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 dia- 

 phragm : 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 post- 

 caval, 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,' indi- 

 cative of the closed oval intercommunicating vacuity in the 



