CRANIAL CAVITY. 



CEREBRAL HEMISPHERES. 



The great longitudinal fissure separates them completely in 

 front and behind but is interrupted mesially below by the cor- 

 pus callosum. Each hemisphere has an external, an internal 

 (mesial), and an inferior surface; the Sylvian fissure divides 

 the latter into an anterior (orbital) and a posterior (tentorial) 

 area. Each hemisphere has four borders; supero-mesial, be- 

 tween the external and internal surfaces ; superciliary, between 

 the external and orbital surfaces; infero-lateral, between the 

 external and tentorial surfaces ; and internal occipital, between 

 the internal and tentorial surfaces. Each has an anterior 

 (frontal pole) and posterior (occipital pole) extremity, and a 

 forward projection (temporal pole), on the under surface, 

 under the Sylvian fissure. Each consists of gray matter (cor- 

 tex) covering a white medullary centre in whose basal part 

 are large gray nuclei (corpus striatum) . [553] 



On the surfaces are convolutions (gyri) separated by fissures 

 (sulci); incomplete fissures are merely superficial; complete 

 fissures involve the whole wall and produce elevations on the 

 ventricular wall. Certain arbitrarily chosen interlobar fissures 

 (fissure of Sylvius, fissure of Rolando, parieto-occipital, 

 calloso-marginal, collateral, and limiting sulcus of Reil) divide 

 the surface into lobes, the frontal, parietal, occipital, temporal, 

 and insula (Island of Reil). [554] 



Fissure of Sylvius. The stem begins at the locus perfo- 

 ratus anticus, in a depression (vallecula Sylvii) on the inferior 

 surface, runs outward to (Sylvian point) the outer surface and 

 divides at once into three limbs. The posterior horizontal 

 limb runs backward and slightly upward for two or three 

 inches and then (ascending terminal piece) turns upward ; the 

 anterior horizontal limb runs horizontally forward for three- 

 fourths of an inch ; the ascending limb runs upward and slightly 

 forward for an inch. [555] 



Limiting Sulcus of Reil. This surrounds the island of 



[37] 



