Dissection of Sheeph Brain, 177 



Choroid Plexuses of the Third Ventricle^ and resemble tlie 

 like parts in the lateral ventricles. On either side of this 

 Third Ventricle are the Optic Thalami ; in front are the ante- 

 rior Crura of the Fornix, with the anterior Commissure of the 

 Cerebrum, lying in front of them and visible in the interval 

 between them ; behind is the Pineal Gland, and in front 

 of, and beneath it, the Posterior Commissure ; crossing the 

 centre of the space from one Optic Thalamus to the other 

 is the Middle or Soft Commissure. 



The Third Yen tricle communicates with the other ventricles 

 of the Brain in the following way : In front it joins each 

 lateral ventricle through the Foramen of Monro : and behind, 

 by a passage which is called the aqueduct of Sylvius, beneath 

 the posterior commissure, it joins the fourth ventricle. At 

 the lower part in front there is a deep pit, which leads down- 

 wards to the funnel-shaped cavity of the infundibulum [iter 

 ad infundibulum). 



It has been shewn that the Thalami Optici enter into the 

 lateral boundaries of both the lateral and third ventricles, 

 that they are separated from the Corpora Striata by the groove 

 in which is the Taenia Semicircularis, and are partly covered 

 by the Fornix : it will now be noted that along the upper 

 part of their inner borders lie the peduncles of the Pineal 

 Gland. The optic tracts which have already been referred to 

 in connection with the base of the Cerebrum may be traced 

 back to the Thalami : each tract, somewhat cylindrical towards 

 the Optic Commissure, becomes flattened and broader as it 

 approaches the Thalamus, and makes a bend as it turns round 

 the Crus Cerebri to reach the back part of that body. Near 

 this bend (which is called the Genu or knee), and to the outer 

 side of the Corpora Quadrigemina are placed two small, oblong, 

 and flattened eminences connected with the posterior extrem- 

 ity of the Optic tract : these are called the Corpora Geniculata. 



The four rounded eminences placed in pairs, and situated 



A A. 



