158 COMPARATIVE MORPHOLOGY OF VERTEBRATES. 



forms a well-developed eye (fig. 151), lying just beneath the skin and connected 

 with the brain by more or less rudimentary nerves. In some the pinealis also 

 shows eye-like features. 



The optic lobes are distinct from each other. The cerebellum is usually 

 small (fig. 159), but in the crocodilia (fig. 151), it attains considerable size. In 

 all reptiles there is a thicker central portion and thinner lateral parts, an approach 

 to the differentiation into vermis and flocculi found in birds. There are no 

 special features in the medulla calling for notice. 



AVES. The bird's brain (fig. 161) is short, broad and highly specialized. The 

 smooth cerebral hemispheres are large, their size being due more to the enormous 

 corpora striata than to enlargement of the pallium, which is comparatively thin, 

 while the olfactory lobes are very slightly developed, in correlation with the deficient 

 powers of smell. The large cerebellum extends forward between the hinder ends 



FIG. 161. Brain of golden eagle, Aquila chrysatos, after Herrick. c, cerebrum; cl, cere- 

 bellum;/, flocculus; mo, medulla oblongata; ol, optic lobes; on, optic nerve. 



of the cerebrum, thus forcing the optic lobes into a lateral position and completely 

 covering the 'twixt-brain. The epiphysial structures are large but rudimentary in 

 character, the pinealis extending up in the angle between cerebrum and cere- 

 bellum. Below, the hypophysis completely hides the infundibulum. The large 

 cerebellum has its median portion transversely furrowed, this constituting the 

 vermis, while the smaller lateral lobes, which vary in extent, form the flocculi. 

 The myelencephalon is very short and the fossa rhomboidea is covered by the 

 cerebellum. 



MAMMALS. The brain in the mammals becomes exceedingly complex. Only 

 the most important features and those of general occurrence will be noted here. 

 Most marked are the large size of the cerebellum and the still greater development 

 of the cerebrum, correlated with the great increase in mental powers. The cere- 



