102 AVES. 



of the hemisphere ; over the third ventricle the partition between the two lateral 

 ventricles is composed of two layers of radiated medullary fibres, and is very similar in 

 form to the septum lucidum, and at its posterior or broader part diverges from the 

 middle line, and leaves a triangular space. The posterior wall, which is a continuation 

 of the septum, is very thin, and is extended over the third ventricle like the former ; 

 pillars from the anterior part pass down, and are inserted into, or joined with, the 

 optic commissure. The part of the hemisphere projecting into this cavity, is termed 

 the striated body. At the anterior part there are two cords proceeding from the 

 hemispheres, and passing just above the optic tracts, which are the crura of the brain. 

 Beneath the lateral ventricles there is a substance on each side connected by a 

 commissure, and these appear to be the thalami, between which the third ventricle is 

 situated. The third ventricle communicates with a cavity in each of the optic lobes, 

 and then passes under the cerebellum to the calamus scriptorius. It appears as if the 

 optic lobes and thalami existed, but are more confounded with each other than in 

 mammalia, and thus a different conformation of parts is produced. 



1. Olfactory nerve. 2. Striated body. 3. Radiated septum, forming the middle 

 boundary of the lateral ventricle. 4. Lateral ventricle ; the anterior part is 

 rough, from which much of the striated body has been removed. 



FIG. VII. 



(THE SAME.) 



1. ANTERIOR pedicles of the radiated lamina. 2. Crus of the brain. 3. Portion 

 of the thalamus extending to the optic commissure. 4. Thalamus of the 

 optic nerve. 5. Cavity of the optic lobe. 6. Ventricle in the cerebellum. 

 7. Lateral lobe of the cerebellum. 8. Crus of the cerebellum. 9. Fourth 



nerve. 



