THE FORE-BRAIN OR PROSENCEPHALON. 5 1 



the base of the brain. Just caudal to the inter-brain is the mid- 

 brain which occupies the tentorial notch of the dura mater; and, 

 situated in the median line, is so overhung by the cerebral hemis- 

 pheres as to reveal only its anterior surface. It resembles the 

 inter-brain in this respect. Inferiorly the mid-brain joins the 

 rhombencephalon. Their plane of union cuts the isthmus (Fig. 



44)- 



In studying the gross structures of the cerebrum it is most 

 convenient to divide it into its embryologic divisions, viz., the 

 fore-brain and the mid-brain. 



SECTION I. THE FORE-BRAIN OR PROSENCEPHALON. 



i. End-brain 



Fore -bra in 



2. Inter-brain 



Cerebral Hemispheres and their connecting 



links 



Corpus Callosum 

 Commissura Anterior 

 Commissura Hippocampi (Fornix). 



Thalami 



Mammillary Bodies (of hypothalamus) 

 Geniculate Bodies (metathalamus) 

 Pineal Body (of epithalamus). 



In order to fix important landmarks and to learn the location 

 and relations of the gross structures of the fore-brain it is neces- 

 sary to study in detail the topography of the exterior surface and 

 the interior surface. It is that with which the present section 

 deals. For the minute anatomy of the cerebral structures, see 

 Section III of the Cerebrum. 



EXTERIOR SURFACE OF FORE-BRAIN. 



The exterior surface of the fore-brain is composed of a thin 

 sheet of gray matter varying in thickness from one-sixth to one- 

 quarter of an inch. That gray matter forms a bark-like cover- 

 ing for the underlying white substance and is, therefore, called 

 the cortex (Figs. 34 and 35). It is thrown into irregular elongated 



