690 



THE XER VOL'S SYSTEM 



From what has been said, it follows tliat the internal pavieto-occipital and calcaiine fissuivs 

 form bj' their union a Y-shai)ed titrure. The hinder part of the stem of the Y and the fore ijart 

 of the ealcarine tissure i)roduL-e an elevation within the i)OSterior corim of the lateral ventricK- 

 known as the hippocamims minor. It has been recently shown that in its (levelopmeut the stem 

 of the Y may belong to the parieto-occipital fissure alone, or to the ealcarine alone, or may be 

 common to both. (Cunningham.) 



Tlu' callosal fissure is a deep furrow which follows the curve of the corpus cal- 

 losuni, being placed between that body and the gyrus fornicatus. It commences 

 below the rostrum of the corpus callosum and termmates behind the splenium, 

 where it becomes continuous with the dentate fissure. 



The dentate or hippocampal fissure extends from the splenium of the corpus 

 callosum to tlie hooked extremity (uncus) of the uncinate gyrus. It produces an 

 elevation in the descending cornu of the lateral ventricle, which is termed the 

 hipi^ocanijius major. 



The collateral fissure is common to the occipital and temporal lobes. It passes 



Fig. 411— Convolutions and Fissures on the Mesial and Tentorial Surfaces of the 



Hemisphere. 



PARACEXTRAL LOBULE 



PR.^CU\E 



SULCUS SI 

 PARI ETA 



PARIKTu- 



OCCIPITAL 



FISSURE 



SULCUS PARACEXTRALIS 



CUXEUS 



CiL- 

 CARIM 

 FISIX III 



CALLOSO-MARGIXAL FISSURE 



3IAROIXAL 



COXVOLUTIOX 



FORXICA TUS 



LOB UL US LI^ i.l Al.l^ 



IXFERIOR OCCIPITO-TEMPORAL / 



COXVOLUTIOX I 



D EX TATE FISSURE 



FISSURE OF SYLVIUS 



\CISURA TEMPORALIS 



UXCUS 



IMPRESSIO PETROSA TEXTORIAL GROO VE 



from a point on the under surface of the temporal lol>e, near its apex to the 

 occipital pole of the hemisphere. The reverse of this fissure appears as an elevation 

 (the eminentia collateralis) in the descending cornu of the lateral ventricle. 

 The follow-ill*'- convolutions appear on the mesial and tentorial surfaces:— 

 The marginal convolution commences below the rostrum of the corpus callosum 

 and occui.ies tin- area of the mesial surface between the calloso-margmal fissure and 

 the margin of the hemis].here as far as the iiaracentral sulcus. The latter separates 

 it from the paracentral lobule. It is continuous around the margin ot the hemi- 

 sphere with the gyrus rectus, the internal orbital, and the superior frontal con- 

 volutions. It is marked bv tertiary fissures along its whole course, m particular 

 by a fissure which runs for "some distance parallel to the calloso-margmal sulcus 



The paracentral lobule is ])ounded in front by the paracentral sulcus; below 

 and beViind bv the calloso-marijinal fissure. It is continuous around the margin ot 

 the hemisi)here with the tuscending frontal and ascending jiarietal convolutions; 

 but as it is connected with the former by a much In'oader band than with the latter. 



