THE CEREBRUM OR PROSENCEPHALON. 



153 



of the opposite side through strong commissural fibers. These bundles all 

 cross the median line at one place, designated the Commissura anterior. 

 This commissure lies in the Lamina terminalis near the base, and is ex- 

 ceedingly constant (Pigs. 18, 76, and 100). The various bundles are best 

 known at present in the reptiles. Everything now known indicates that the 

 relations are the same in the other vertebrates as in reptiles. 



The commissures of the olfactory apparatus are shown schematically 

 in Fig. 101. 



II. THE CORPUS STRIATUM. 



The Corpus striatum lies above the olfactory apparatus. It is a some- 

 what ovoid body which projects up into the ventricle of the cerebrum from 



.Tr.septomesoce/ih. 



— Omuniss. fjallii post. 

 .... Comm.jiaUii aiit. 



s yGmwiiss. a/zf. 



Fig. 101. — Schema of the commissures of the olfactory mechanism of the 

 reptile (compare Fig. 98). Pars epistriat., Epistriatic commissure. Pars cortical., 

 Commissure of olfactory cortex of one hemisphere with that of other. Pars 

 olfact., Ramus eonnectens Lobi olfactorii. 



the base of the cerebrum, occupying the same place in all animals from the 

 fishes to man. 



It is not usually to be seen in the uncut brain, because it is covered in by 

 the brain-mantle, and lies really in the floor of the enmantled ventricle. 

 Only in fishes, where the mantle is represented by a thin membrane, is it 

 to be recognized through the mantle. In this ease it forms what is called 

 the frontal lobe. The more highly developed the mantle, — as in mam- 

 mals, — the more unimportant appears the structure — so large relatively 



