PHYLUM CHORDATA 



447 



Rol 



or less completely 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 cere- 

 bral hemispheres are 

 well developed in all. 

 The mid-brain consists 

 usually of two closely- 

 approximated oval optic 

 lobes. The cerebellum 

 is always of small size, 

 except in the Crocodilia 

 (Fig. 254), in which it is 

 comparatively highly de- 

 veloped, and consists of 

 a median and two lateral 

 lobes. 



The eyes are relatively 

 large, with a cartilaginous 

 sclerotic in which a ring 

 of bony plates is de- 



FIG. 254. Brain of Alligator, from above 

 B. ol. olfactory bulb ; G. p. epiphysis 

 HH. cerebellum ; Med. spinal cord ; MH 

 optic lobes ; NH. medulla oblongata 

 VH. cerebral hemispheres ; / XI. cranial 

 nerves ; i, 2. first and second spinal 

 nerves. (From Wiedersheim's Comparative 

 Anatomy.} 



