THE CEEEBEUM OR PKOSENCEPHALON. 



165 



development of the striatum (see Fig. 105, B). Between the two projections 

 remains the groove, which has been designated the Fovea collateralis. 



Somewhat more complicated than the arrangement of the outer aspect 

 of the hemispheres is that of the median wall. In the amphibia this wall has 

 undergone so little differentiation, that in certain species — indeed, in differ- 

 ent specimens of the same species — it may be grown to the adjacent wall of 

 the other hemisphere for a greater or less distance. 



Such is not the case in reptiles. While all the features to be here de- 

 scribed are present in amphibia in a rudimentary form, it is only in the 

 highly organized reptilian brain that they come out into prominence. Here 

 one can easily make several subdivisions, subdivisions which, as will be 

 brought out later in the description of the mammalian brain, will serve as 

 important points of departure in following its further development. 



Fig. 114. — Inner wall of a hemisphere of the reptilian brain: 

 from Tarantis griseus. 



1. The median surface of the olfactory apparatus near the base: Area 

 parolfactoria. In reptiles there are prominent aggregations of ganglia here, 

 which give rise to bundles of fibers. 



2. Posterior to this and somewhat farther dorsal lies that portion of the 

 median wall designated the Septum, which also contains a ganglion in rep- 

 tiles, in birds is strongly atrophied, while in mammals, again, it contains a 

 small ganglion and is called the Septum pellucidum,. 



3. Dorsal to the two portions named is the cortical portion of the inner 

 wall. 



In the dorsal portion of the area parolfactoria there begins regularly 

 a deep sulcus, which, running to the Lamina terminalis in the upper margin 



