5 



THE BRAIN 



Dissection. Each vena terminalis should now be divided as it unites 

 with the internal cerebral vein. The apex of the tela chorioidea should 

 then be seized with the forceps and pulled posteriorly, till the whole 

 structure is reversed. The entire upper surface of the thalamus on 

 each side is thus exposed, and, between the thalami, is seen the third 

 ventricle. The epithelial roof of this ventricle, which is invaginated into 

 the cavity by the chorioid plexuses of the third ventricle on the under 

 surface of the tela, is torn away with the tela. The basal part of the tela 

 is intimately connected with the pineal body, which lies on the mesen- 

 cephalon behind the third ventricle. Care therefore must be taken to 

 extricate this body from the pia mater ; otherwise it is sure to be pulled 

 away. 



THE THALAMI AND THE THIRD VENTRICLE. 



Thalamus. The thalamus is a large mass of grey matter 

 which lies obliquely across the path of the pedunculus cerebri 

 as it ascends into the hemisphere. The smaller anterior end 



Corpus callosun 

 Lateral ventricle 

 Caudate nucleus ; 

 Fronto-occipital fasciculus i 



Chorioid plexus 



Striae on corpus callosum 



Longitudinal fissure 

 / "; ; Septum pelluciduni 



Vena termiualis 

 Subthalamic body 



Thalamus 



f 3rd ventricle 

 Chorioid plexus 

 Red nucleus 



FIG. 205. Frontal section showing immediate relations of Lateral and 

 Third Ventricles. (Part of Fig. 217 enlarged.) 



of the thalamus lies close to the median plane, and is separ- 

 ated from the corresponding part of the opposite side only 

 by a very narrow interval. The enlarged posterior ends of 

 the two thalami are placed more widely apart ; and in the 

 interval between them, the corpora quadrigemina are situated. 

 In their anterior two-thirds, the two thalami lie close together, 

 but are separated by a deep median cleft, the third ventricle 



