412 



THE NERVOUS SYSTEM. 



some other centres of gray matter not so distinct, such as the 

 gray matter on the floor of the fourth ventricle with which the 

 auditory nerve is connected, the most philosophical theory is 



FIG. 146. 



Dissection of brain, from above, exposing the lateral, fourth, and fifth ventricles, 

 with the surrounding parts (from Hirschfeld and Leveill6). %. a, anterior part, or 

 genu of corpus callosum; 6, corpus striatum; &', the corpus striatum of left side, dis- 

 sected so as to expose its gray substance ; c, points by a line to the tsenia semicircu- 

 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 an- 

 terior 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 (just visible) and the pineal gland, the two crura of which 

 extend forwards along the inner and upper margins of the optic thalami ; h and i, 

 the corpora quadrigemina ; k, superior crus of cerebellum ; close to k is the valve of 

 Vieussens, which has been divided so as to expose the fourth ventricle ; /, hippo- 

 campus major and corpus fimbriatum, or tsenia hippocampi ; m, hippocampus minor ; 

 n, eminentia collateralis ; o, fourth ventricle ; p, posterior surface of medulla oblon- 

 gata ; r, section of cerebellum ; s, upper part of left hemisphere of cerebellum exposed 

 by the removal of part of the posterior cerebral lobe. 



undoubtedly that which has been so ably enunciated by Dr. 

 Carpenter. He supposes these ganglia to constitute the real 



