188 TOPOGRAPHICAL ANATOMY OF THE 



band mainly concerned in connecting the two hemispheres with each 

 other. It is not co-extensive with the hemispheres, but coincides with 

 the middle two-fourths of these structures. 



The dorsal surface of the corpus callosuui has a slight convexity 

 longitudinally, but is concave from side to side. Numerous transverse 

 lines (stride transversa') show that it is mainly composed of commissural 

 fibres, though faint longitudinal markings, corresponding to the stria? 

 longitudinales of the human brain, may be detected. The ventral 

 surface forms the roof of the lateral ventricles, and in the median plane 

 is connected with the septum pellucidum, a partition separating the 

 cavities of the two ventricles. The lateral boundaries of the corpus 

 callosum are lost in the white substance of the hemispheres. 



The main part of the corpus callosum is known as the truncus 

 corporis callosi. Its posterior end is thickened and forms the 

 spleniutn^ corporis callosi ; while the anterior end, as an examination 

 of the sagittal median section will show, is abruptly bent at the 

 genu ^ corporis callosi, from which is continued a recurved, tapering 

 (in section) rostrura ^ corporis callosi connected in its turn with the 

 lainina terminalis, a thin sheet of grey matter that lies dorsal to the 

 optic chiasma and is continuous with the tuber cinereum. 



Dissection. — The interior of the lateral ventricle must now be exposed. 

 Make a longitudinal incision through the corpus callosum some three or 

 four mm. from the middle line, and tlien remove that part of tlie body 

 which is lateral to the incision by tearing it away with either forceps or 

 the end of the handle of the scalpel. When both ventricles have tlius 

 been opened, a narrow strip of corpus callosum will be left undisturbed. 



Two cornua proceed from the main part of the ventricle now exposed. 

 One of these is anterior in position and can be followed without much 

 difficulty. The course of the other (inferior) cornu must be disclosed by 

 the piecemeal removal of portions of the hemisphere ; and in doing this it 

 is well to remember that the cornu curves at first in a lateral, backward 

 and ventral direction, and that later its course is medialwards and 

 forwards. 



A proper understanding of the lateral ventricle and its boundaries will 

 be aided by the dissection of the cavity from the medial aspect. To do 

 this, remove the corpus callosum and the immediately adjoining part of 

 the hemisphere from the hemi-sected brain. Though the anterior cornu 

 may be completely investigated in this specimen, it is better to do no 

 more than expose the first part of the inferior cornu. 



The lateral ventricle (Ventriculus lateralis). — The lateral 

 ventricle represents the cavity of the vesicle from which the hemisphere 

 originally developed, and is in communication with the third 



^ fipleniiim [L.], a jalaster or patch ; cnr\i-)VLov (splenion) [Gr.], a bandage, 



comi^ress of linen. 

 ^ Genu [L.], knee. 

 2 Rostrum [L.], the bill or beak of a bird. 



