522 



THE NERVOUS SYSTEM. 



made on the organs or tissues with which (by means of 

 Fig. 146.* 



* Fig. 146. Dissection of brain, from above, exposing the lateral, 

 fourth, and fifth ventricles, with the surrounding parts (from Hirsch- 

 feld and Leveille). i. a, anterior part, or gcnu of corpus callosum ; 

 Z>, corpus striatum ; ', the corpus striatum of left side, dissected so as 

 to expose its grey substance ; c, points by a line to the tsenia semicu- 

 laris ; d, optic thalamus ; e, anterior pillars of fornix divided ; below 

 they are seen descending in front of the third ventricle, and between 

 them is seen part of the anterior commissure ; in front of the letter e 

 is seen the slit-like fifth ventricle, between the two lamina of the 

 septum lucidum ; /, soft or middle commissure ; g is placed in the pos- 

 terior part of the third ventricle ; immediately behind the latter are 

 the posterior commissure (just visible) and the pineal gland, the two 

 crura of which extend forwards along the inner and upper margins of 

 the optic thalami ; li and i, the corpora quadrigemina ; k, superior 

 crus of cerebellum ; close to k is the valve of Vieussens, Avhich has 

 been divided so as to e xpose the fourth ventricle ; I, hippocampus 



