64 DISSECTION OF THE CAT 



behind and below the body of the fornix. The 

 margins of this membrane are very vascular, and 

 are known as the choroid plexuses. These plex- 

 uses are continued through the foramina of Munro 

 to form the choroid plexuses of the lateral ven- 

 tricles. The velum is somewhat thickened poste- 

 riorly to form the pineal gland. (Plate VII., c.) 



12. The Third Ventricle, before mentioned, is the 

 very narrow cavity of the brain lying between the 

 optic thalami. It is bounded above by the velum 

 interpositum, and below by the lamina cinerea, 

 corpora albicantia, crura cerebri, and the infundib- 

 ulum, and with the cavity of the latter it is contin- 

 uous. It opens anteriorly into the two lateral ven- 

 tricles through the foramina of Munro. (Plate 

 VII., c.) 



Make a median, vertical, longitudinal section 

 through the remaining portion of the brain. 



13. The Anterior Commissure is a delicate trans- 

 verse band of fibres, passing between the two 

 hemispheres, in front of the anterior pillars of the 

 fornix. It connects the two corpora striata. The 

 lamina cinerea passes between it and the optic 

 chiasma. (Plate VII., c.) 



14. The Middle or Soft Commissure is a much 

 larger band of transverse fibres and cells connect- 



O 



ing the optic thalami. It passes across the upper 

 part of the third ventricle. (Plate VII., c.) 



15. The Posterior Commissure joins the dorsal por* 



