THE BRAIN IN THE SEPARATE CLASSES 



169 



show the beginnings of a temporal lobe (see fig. 178 near /// and IV nerves). 

 The olfactory lobes are merged in the hemispheres and the nerve extends for- 

 ward from them (see p. 183). The corpora striata are large, reducing the lateral 

 ventricles to slit-like spaces. The great development of the cerebrum and the 

 optic lobes partially covers the roof of the diencephalon, which may develop 

 both the parietal organ and the pinealis, the latter in some forms {e.g., Scelo- 

 porus) showing an eye-like structure. The parietal eye is well developed in all 



i'lG. 177. Fig. 178. 



I Fig. 177. — Brain of Iguana tuberculata (Princeton, 2293). Compare fig. 194. 

 ^0>^^ f^iG. 178. — Side and dorsal views of brain of young alligator, After Herrick. c, 

 r cerebrum; c/, cerebellum; e, epiphysial structures; A, hypophysis; t, infundibulum; 0/, 

 optic lobes; II-XII, cranial nerves. 



lacertilia, its position being readily recognized on the top of the head. In 

 other groups it is rudimentary. The great development of the thalami reduces 

 the third ventricle to a vertical slit, and in some groups the walls of the two 

 sides may unite across the median line near the middle of the ventricle, form- 

 ing an 'intermediate mass' (soft commissure) which reappears in the mammals. 

 The mid-brain bears paired optic lobes. The cerebellum has a considerable 

 range of form. In the alligators it develops on either side a lobe (shown to the 



