98 THE ANATOMY OP VERTEBRATED ANIMALS. 



much longer period tlian tliat between the ventricles — and 

 the aperture by which the am-icles communicate is called 

 thefm-amen ovale. 



In the adult state of Aves and Mammalia, the foramen 

 ovale is closed ; there is no direct comnninication between 

 the arterial and venous cavities or trunks ; there is only one 

 aortic arch ; and the pulmonary artery alone arises from the 

 right ventricle. In the Crocodilia, the auricles and ven- 

 tricles of opposite sides are completely separate ; but there 

 are two aortic arche.s, and one of these, the left, arises from 

 the i-ight ventricle along with the pulmonary artery. In all 

 Reptilia, except Crocodiles, there is but one ventriciilar 

 cavity, though it may be divided more or less distinctly into 

 a cavum venosum and a cavmn arteriosum. The auricles are 

 completely separated (except in some Chelonia), and the 

 blood of the left am-icle flows directly into the cavum arterio- 

 sum, while that of the right passes immediately into the 

 cavum venosum. The aortic arches and the pulmonary artery 

 all arise from the cavum venosum (or a special subdivision 

 of that cavity called the cavum pulmonale) ; the ostium of the 

 pulmonary artery being farthest from, and that of the right 

 aortic arch nearest to, the cavtim artenosxmn. 



In all Amphibia, the sjjongy interior of the ventricle is 

 undivided, and the heart is trilocular, though the auricular 

 septum is sometimes small and incomplete. In all Pisces, 

 except Lepidosiren, there is no auricular septum. In Am- 

 phioxus the heart remains in its primitive state of a simple, 

 contractile, undivided tube. 



In the Ganoidei, the Elas^iiohrancliii, and the Amphibia, 

 the walls of the enlarged commencement of the cardiac 

 aorta, called the bulbus aortce, contain striped muscular 

 fibre, and are rhythmically contractile. 



The Ganoidei and Masmobranchii possess, not merely the 

 ordinary semilunar valves, at the junction between the 

 ventricle and the cardiac aorta, bvit a variable number of 

 additional valves, set, in transverse rows, upon the inner 

 wall of the aortic bullD. 



The change of position which the heai-t and the great 



