THE CEREBRUM 



445 



parts of the chorioidal fissures, which have been studied already 

 in connection with the inferior horn of the lateral ventricle 

 (P- 437)- 



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 

 backwards, till the whole structure is reversed. As that is 

 done, care must be taken to avoid injury to the attachments of 

 the pineal body, which is enclosed in a fold of the posterior part 

 of the lower layer of the tela. When the tela chorioidea has 

 been displaced backwards to the level of the mid-brain, the entire 

 upper surface of the thalamus on each side is exposed, and, between 

 the thalami, the cavity of the third ventricle is seen. The epithelial 

 roof of that 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 THALAMI AND THE THIRD VENTRICLE. 



Thalamus. The thalamus is a large mass of grey matter 

 which lies obliquely across the path of the corresponding 



Corpus callosum Chorioid plexus 



Lateral ventricle 

 Caudate nucleus j 

 Fronto-occipital fasciculus i 



Striae on corpus callosum 

 ; Longitudinal fissure 

 / 1 ! Septum pellucidum 



Vena terminalis ' 

 Hypothalamic body 



3rd ventricle 

 Chorioid plexus 



Thalamus Red nucleus 



FIG. 175. Frontal section showing immediate relations of Lateral and 

 Third Ventricles. (Part of Fig. 188 enlarged. ) 



pedunculus cerebri as it ascends into the hemisphere. In 

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

 but are separated by a deep median cleft called the third 

 ventricle ; the posterior thirds are further apart from one 



