PHYLUM CHORDATA 



449 



auricles, as in the Amphibia, the right receiving the venous 

 blood from the body, the 



left the oxygenated blood Miff /« — B.6Z 



brought from the lungs by 

 the pulmonary veins. But 

 a vital point of difference 

 between the heart of the 

 reptile and that of the am- 

 phibian is that in the 

 former the ventricle is al- 

 ways more or less com- 

 pletely divided into right 

 and left portions. In all the 

 Lacertilia, Ophidia, and 

 Chelonia the ventricle is 

 incompletely divided by 

 a septum which does 

 not entirely cut off the 

 two portions of the 

 cavity from one another. 

 But in the Crocodilia 

 the cavity is completely 

 divided, so that we may 

 speak of distinct right 

 and left ventricles. 



The brain of Reptiles 

 is somewhat more highly 

 organised than that of the 

 Amphibia. The cerebral 

 hemispheres are well de- 

 veloped in all. The mid- 

 brain consists usually of 

 two closely approximated oval optic lobes. The cerebellum 



Fie. 270. — Brain of alligator, from above. 

 B. ol., olfactory bulb ; G. /, epiphysis : 

 HH, cerebellum ; Med , spinal cord ; ilff, 

 optic lobes ; NH , medulla oblongata ; 

 I'N, cerebral hemispheres; / — XI, cra- 

 nial nerves ; 1,2, first and second spinal 

 nerves. (After Wiedersheim. ) 



