746 



THE NERVOUS SYSTEM. 



proper. This "upward prolongation" of the floor is known as the "anterior 

 boundary " of the ventricle. 



The Optic Thalamus. Each optic thalamus is a large oblong mass of, chiefly, 

 gray matter. It has two rounded extremities, anterior and posterior, and four 

 surfaces, superior, inferior, external, and internal. 



The inferior surface rests upon, and is united with its corresponding part of 

 the tegmentum. The external surface lies in contact with the internal capsule of 

 the hemisphere. Its internal surface forms the lateral boundary or wall of the 



Anterior cornu 

 Fifth ventricle 



Septum 

 pellucidum 



Orifice of 

 infundibulum 



Tsenia semicirc. 



Peduncle of 

 'pineal gland 



Orifice of Syl- 

 ^/wan aqueduct 



^Epiphysis 



Fillet (lat.) 



'trise. acusticx 



Intermed. lat. furrow 

 Post. med. fissure 



FIG. 441. Superior surface of inter-brain ; dorsal surfaces of mid-brain, pons, and medulla. Most of the 

 cerebral hemispheres and cerebellum are removed, X i- (Gegenbaur.) 



third ventricle (Figs. 447, 442, 441). Its upper surface is free, and is traversed 

 by a groove from behind forward and inward. The portion external to this 

 groove is seen in the floor of the body of the lateral ventricle, but it is covered 

 by a layer of epithelium continuous with that lining the lateral ventricle. It is 

 marked in front by an eminence, the anterior tubercle. The portion of the upper 

 surface internal to the groove is covered by the velum interpositum. 



The posterior extremity of the optic thalamus projects beyond the level of the 

 corpora quadrigemina, and forms a well-marked prominence, the posterior tubercle 

 or pulvinar in close connection with which are two small rounded eminences, the 

 internal and external geniculate bodies, the internal lying in the groove between 

 the dorsally projecting pulvinar and side of the mid-brain, the external being placed 



