CHAPTER III. 

 THE CEREBRUM. 



The cerebrum with its great hemispheres is that part of the 

 brain which especially characterizes man. In man only do the 

 hemispheres reach such predominant development. Though 

 they are mere outgrowths of the anterior brain-vesicle in the 

 beginning, they completely overshadow all other parts of the 

 brain by the seventh month of embryonic life, extending farther 

 forward, backward and lateralward than any other part. Within 

 the cerebral hemispheres lies the physical basis of all mental func- 

 tion; they constitute the central mechanism of thought and con- 

 sciousness. 



Reference to the table given above shows that the cerebrum 

 is made up of three parts: (i) The end-brain, which includes 

 the cerebral hemispheres and their connecting links; (2) the 

 inter-brain, comprising the thalami and their associated nuclei, 

 which with the former constituted the fore-brain; and (3) the 

 mid-brain (Figs. 17, 18, and 27). The cerebrum is an ovoid 

 mass, flattened inferiorly, which fills the vault of the cranium and 

 rests, below, upon the floor of the cranial cavity in the anterior 

 and middle fossas and upon the tentorium cerebelli over the 

 posterior fossa (Fig. 2). Viewed from above, it is sufficiently 

 round to suggest a sphere; and, being divided in the median line 

 by the longitudinal fissure, the lateral halves are called hemis- 

 pheres. The most anterior point is the frontal pole, and the 

 most posterior is the occipital pole (Fig. 22). In the floor of the 

 longitudinal fissure of the cerebrum the corpus callosum can be 

 seen joining the hemispheres together; and beneath it, concealed 

 from view, are the fornix and anterior commissure. 'Those are 

 the connecting links, proper, of the hemispheres (Figs. 34, 36 and 

 37). Inferior to them is found the inter-brain. The latter form 

 an additional union of the hemispheres, as may be seen by viewing 



SO 



