202 



REPTILIA. 



Ss 



epiglottis is present in many Tortoises, Snakes, and Lizards. The 

 Geckos and Chaniseleons alone have a vocal apparatus. The renewal 

 of the air necessary for respiration is, except in the Chelonia, always 

 effected by aid of the ribs. 



The circulatory organs (fig. 60) present various grades of develop 

 ment, even to the complete division of the heart, and to the separation 



of the venous and arterial blood. 

 Not only are there two auricles 

 which are distinct even exter- 

 nally, but the ventricle also is 

 divided into a right and left 

 chamber. The partition wall of 

 the ventricles is indeed per- 

 forated in Snakes, Lizards, and 

 Chelonians ; but in the Croco- 

 diles it is complete, and effects 

 the separation into a right and 

 left ventricle. In the first cases 

 the pulmonary arteries and the 

 aortic trunks arise from the 

 wide thin-walled right division 

 of the ventricle. In the Croco- 

 diles, on the other hand, the 

 pulmonary arteries and the 

 aortic trunks have a separate 

 origin (fig. 633). The complete 

 number of aortic arches is 

 present only during the foatal 

 life ; in later life their number 

 becomes much reduced. Ori- 

 ginally five pairs of vascular 

 arches as also in Birds and 

 Mammals are present ; they 

 embrace the gullet and join to 



form the two roots of the aorta. Most of them, however, undergo 

 reduction, losing their connections with each other, so that finally 

 each aortic root (Saurians) arises from two vascular arches, or is 

 the prolongation of a single aortic arch. The aorta, which passes 

 out from the heart, is divided into three trunks a right and left 

 aorta and a pulmonary artery each with a separate opening 

 into the ventricle \i.e., three distinct arterial trunks leave the 



Jf 



FIG. 633. Heart and large vascular trunks of 

 Alligator lucius seen from the ventral side 

 and partly opened (after Gegenbaur). D, 

 right auricle ; S, left auricle ; O, ostium 

 venosum of the right auricle ; Oo, auriculo- 

 ventricular aperture; Ha, bulbus arterio- 

 sus ; C, carotis primaria ; S<1, Ss, subclavian 

 arteries; Ad, right aortic arch; As, left 

 aortic arch ; P, pulmonary artery ; f, con- 

 nection of right with left aortic arch ; M, 

 mesenteric artery ; PC, connection of the 

 heart with the pericardium; FP, position 

 of the foramen Panizza?. 



