162 



ANATOMY OF THE CBNTEAL NEETOUS SYSTEM. 



lamina. The dorsal portion is directed posteriorly and may be designated 

 as the Polus occipitalis pallii. 



The ventral projection, which is present only in a rudimentary form in 

 amphibians and reptiles (Fig. 113), should be called Polus temporalis. Into 

 both these poles the ventricular cavity extends, forming a posterior horn 

 and an inferior horn. 



Tfor^fK "^::)Vf Off 



Fig. 108. — Sagittal section of a selachian brain (the ray). 



The nearly ovoid hemispheres of the amphibian correspond most closely 

 to this schematically described brain. But even in the reptiles the outer 

 form manifests quite marked variations in the development, according to 

 the families. When one finally passes up through the birds and mammals 

 he soon meets the widest variations in form. 



Fig. 109. — Sagittal section of an amphibian brain. 



At first there is, in amphibians, a hardly noticeable groove between the 

 olfactory lobe and the mantle, running outward and downward on the mar- 

 gin of the mantle, called the Fovea limhica. This groove, separating the 

 olfactory apparatus from the mantle, is always clearly marked in mammals. 

 The development of the individual poles offers essential differences. Some 

 have suggested for the Polus frontalis of the lower vertebrates the term 



