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NEUROLOGY 





The Longitudinal Cerebral Fissure (fissuracerebrilongitudinalis; great longitudinal 

 fissure} contains a sickle-shaped process of dura mater, the falx cerebri. It front 

 and behind, the fissure extends from the upper to the under surfaces of the hemi- 

 spheres and completely separates them, but its middle portion separates them for 

 only about one-half of their vertical extent ; for at this part they are connected across 

 the middle line by a great central white commissure, the corpus callosum. 



In a median sagittal section (Fig. 720) the cut corpus callosum presents the 

 appearance of a broad, arched band. Its thick posterior end, termed the splenium, 

 overlaps the mid-brain, but is separated from it by the tela chorioidea of the third 



ventricle and the pineal body. Its anterior 

 curved end, termed the genu, gradually tapers 

 into a thinner portion, the rostrum, which is 

 continued downward and backward in front of 

 the anterior commissure to join the lamina 

 terminalis. Arching backward from immediately 

 behind the anterior commissure to the under 

 surface of the splenium is a second white band 

 named the fornix: between this and the corpus 

 callosum are the laminae and cavity of the 

 septum pellucidum. 



Surfaces of the Cerebral Hemispheres. Each 

 hemisphere presents three surfaces: lateral, 

 medial, and inferior. 



The lateral surface is convex in adaptation to 

 the concavity of the corresponding half of the 

 vault of the cranium. The medial surface is 

 flat and vertical, and is separated from that 

 of the opposite hemisphere by the great longi- 

 tudinal fissure and the falx cerebri. The inferior 

 surf ace is of an irregular form, and may be divided 

 into three areas : anterior, middle, and posterior. 

 The anterior area, formed by the orbital sur- 

 face of the frontal lobe, is concave, and rests on 

 the roof of the orbit and nose; the middle area 

 is convex, and consists of the under surface of 

 the temporal lobe: it is adapted to the corre- 

 sponding half of the middle cranial fossa. The 

 posterior area is concave, directed medialward 

 as well as downward, and is named the tentorial 

 surface, since it rests upon the tentorium cere- 

 belli, which intervenes between it and the upper 

 surface of the- cerebellum. 



These three surfaces are separated from 

 each other by the following borders: (a) 



supero-medial, between the lateral and medial surfaces; (6) infero-lateral, between 

 the lateral and inferior surfaces; the anterior part of this border separating the 

 lateral from the orbital surface, is known as the superciliary border; (c) medial 

 occipital, separating the medial and tentorial surfaces; and (d) medial orbital, 

 separating the orbital from the medial surface. The anterior end of the hemi- 

 sphere is named the frontal pole ; the posterior, the occipital pole ; and the anterior 

 end of the temporal lobe, the temporal pole. About 5 cm. in front of the occipital 

 pole on the infero-lateral border is an indentation or notch, named the preoccipital 

 notch. 



The surfaces of the hemispheres are moulded into a number of irregular emi- 



Fio. 725. Lateral surface of left cerebral 

 hemisphere, viewed from above. 



