Chap. I. 



VASCULAR SYSTEM. 



285 



SECTION XII. 



VASCULAR SYSTEM. 



The heart of the Turtles lie.s ju.st above the liver. It is broad, nearly trian- 

 gular, the wide basis of the triangle extending across the body. It is inclosed in a 

 double sac of the pericardium, and attached to it, at its point, by means of a fold 

 of the pericardium. The plan of its interior structure is the same i)i Turtles as 

 in Ophidians and Sanrians. While in Crocodiles there exists a true septum between 

 both ventricles/ as in Birds and Manunalia, we find in Turtles, typically, only one 

 ventricle.^ 



In a large specimen of Ptychemj's rugosa, (E. ru])riventris,) we had an opportu- 

 nity of studying the beating of the heart. The process is as follows: The auricles 

 are filled simultaneou.sly, one -with a bluisli red, the other with a light red blood. 

 When lilloil to the utmost, they have a triangular sh.-ipe, ^^'ith roiuided corners. But 

 whil(( the auricles are already tlius filling, the heart itself, the ventricle, is grad- 

 ually expanding more and more ; then a sudden contraction of the auricles throws 

 all the Ijlood into the broadly expanded, but empty, ventricle, which thus filled 

 assumes the form of a high co)ie. Immediately after tliis follows the contraction of 

 the ventricle, then lbllo^vs a pause until the auricles are filled again, and the power- 

 ful pump begins its play anew. Tliis goes on about ten times i)i a minute. The 

 rh}thm in its details is as follows: First second, s3^stole of the auricles; .second 

 second, systole of the A^entricle ; third and foiu-th seconds, the ventricle remains 

 contracted ; fifth and sixth seco)ids, the auricles are gradually filling ; seventh 



' TKis difference bepomes, liowover, of less impor- 

 Uince when we reiniirtlier tlio facl. tliat in Crocodiles 

 tliere exists, at tiieir verj' base, a communication be- 

 tween the two trunks which st.art from the two ven- 

 tricles of the heart, causing tliere a similar mixture 

 of tJK' dark and red Idood, outside of tlie heart, a5 

 e.\ist.s, in Turtles, ii\side of the heart. 



" We cannot agree with tiie \ iew generally adopt- 

 ed, tliat this so-called imperfect septum in the heart 

 of Turtles, which seems to divide it into two cnvities, 

 a so-called cavuni arteriosiim and a cavum venosum, 

 is homologous to the perfect se]>tum between the ven- 

 tricles which existij in Mammalia and Birds. The 



fact, that tlic gre.at bloodvessels (the aorta and the 

 arteria puhnoi\alis) start together from tlie cavum 

 vcnosuni, seems to prove that the two cavities in 

 the heart of Turtles, whicli are by no means very 

 marked, do not correspond to the two ventricles in 

 Mammalia and IJirds, but, on the contrary, that, as 

 stated aliove, the ventricle in Turtles is typically 

 one, as in Fishes. Yet this one ventricle of Tur- 

 tles is not any more identical with the one ventri- 

 cle of Fishes llian with the two ventricles of warm 

 blooded Vcrtcbrata, for in Fishes we find only one 

 vessel, the aorta, arising fnim it, wliile in Turtles, both 

 aorta and arteria pulmonalis start togetlier from it. 



