322 ELEMENTARY PHYSIOLOGY. [XXX. 



ventricle; the corpus callosum; the septum 

 lucid urn, deep anteriorly, between the corpus 

 callosum and the fornix ; the pia mater entering 

 the transverse fissure, forming there the velum 

 interpositum which lies underneath the fornix 

 and over the optic thalami ; the anterior pillar 

 of the fornix curving downwards in the direction 

 of the corpus albicans ; the anterior commissure 

 a little in front of the apparent termination of 

 the anterior pillar of the fornix ; the posterior 

 perforated space behind the corpus albicans ; the 

 optic chiasma. 



2. Cut a transverse section of the mid-brain 1 passing 

 a little in front of the pons and through the 

 anterior corpora quadrigemina. Observe 

 a. Ventrally, and a little removed from the 

 median line on each side, the crusta of the 

 cerebral peduncle, it forms a slight project- 

 ing oval mass of transversely cut fibres. 

 I. A thin grey layer, the substantia nigra 

 above the crusta. 



c. The central grey substance around the 

 aqueduct of Sylvius. 



d. The tegmentum, between the substantia 

 nigra and the central grey substance, else- 

 where it does not show distinct boundaries. 



3. Cut a brain through transversely carrying the 

 cut a little in front of the corpus albicans and 



1 The parts described in this and in the succeeding section are 

 much better seen hi a brain which has been hardened in ammonium 

 bichromate than in one hardened in alcohol. 



