524 THE NERVOUS SYSTEM. 



accustomed to consider voluntary, but which really are as 

 Fig. 139.* 



* Fig. 139. Dissection of brain, from above, exposing the lateral, third, 

 fourth and fifth ventricles, with the surrounding parts (from Hirschfeld 

 and Leveille). -|. , anterior part, or genu of corpus callosum ; 6, corpus 

 striatum ; b', the corpus striatum of left side, dissected so as to expose 

 its grey substance ; c, points by a line to the taenia semicircularis ; 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 laminae of the septum lucidum ; /, soft 

 or middle commissure ; g is placed in the posterior part of the third 

 ventricle ; immediately behind the latter are the posterior commissure 

 (j-ust visible) and the pineal gland, the two crura of which extend for- 

 wards along the inner and upper margins of the optic Thalami ; k and , 

 the corpora quadrigemina ; Jc } superior crus of cerebellum ; close to 



