160 



ANATOMY OF THE CENTRAL NEETOUS SYSTEM. 



which join the hemispheres to the striatum traverse the Lamina terminalis 

 (see Fig. 101). In mammals for the first time there arises late in the em- 

 bryonic period, dorsal and anterior to the Lamina terminalis, a new system 

 of transverse fibers destined to connect cortical regions of one hemisphere 

 with those of the other: Corpus callosum. 



The mantle of higher vertebrates is differentiated from those of teleosts 

 and ganoids through a very essential feature. It is no longer simple epi- 



Fig. 106. — Selachian brains, showing the various development of the brain- 

 mantle in different species. A, Brain of Galmis canis ; B, of Raja mlraletus. C, 

 The cerebrum of Carcharias. All are sho\\n in natural size. In J. the Tela 

 chorioidea is removed, giving a glimpse of the ventricle of the Thalamencephalon. 



thelium, but consists of numerous cells which receive and send out nerve- 

 fibers; that is, the mantle has become a nervous mechanism. This mechan- 

 ism, which is not much developed in the amphibians, reaches, in the reptiles, 

 the condition of a well marked brain-cortex, differentiated from the other 

 layers of the mantle. 



