THE BRAIN AND SPINAL COED. 



213 



bounded by three limiting sulci — an anterior, superior, and in- 

 ferior. The rising lips of cortex, which bound the limiting sulci, 

 form the temporal, fronto-parietal, and orbital opercula, and 



occip. lobe 



cereb. vesicle^,, „ ^opticthai. 



• Sylvian dep. 



olf. lobe' \ Pitu!tary 

 optic nerve 



Fig. 174. — Lateral Aspect of the Cerebral Hemisphere during the 2nd month. 



ultimately meet over the submerged area (Fig. 176). The 

 fissure of Sylvius separates the opercula. It will be readily 

 grasped that the development of the corpus striatum prevents 

 the expansion of the insular part of the vesicle, whereas the 

 thin-walled mantle, out of which the other lobes of the brain 

 are developed, expands readily and overwhelms the thickened 



fronto-par.op. 



occip. 



. . . . , cerebellum 



orb. op. / ... \ 

 / island, areas 



olf act: temp: op. 



Fig. 175. — The same Aspect during the 5t'h month. 



area. The corpus striatum begins to form during the 2nd month, 

 hence as earJy as that date the insular depression is visible on 

 the lateral wall of the hemisphere (Fig. 174). 



The lower end of the stem of the Sylvian fissure also indents 



