MAMMALIA 



293 



thin adposed walls which form the septum lucidum. The 

 septum expands below into the body of the fornix, and is 

 crossed above by the transverse fibres of the corpus callosum. 

 Each lateral ventricle extends forwards from the foramen 

 of Monro, and is continued as an anterior horn or cornu, and 

 this is bent downwards to reach the olfactory lobe, becoming 

 reduced in size, and expanding again when it enters the 

 olfactory lobe. The posterior cornu extends backwards and 

 downwards into the temporal lobe. The lateral wall of the 

 anterior cornu is indented by the caudate nucleus of the corpus 



Cerebral 

 hemisphere i ** 



ebellum 



Glf. 



V Medulla 

 vent 



FIG. 138. Longitudinal section of the brain of the sheep. 



striatum, a structure which is completed by the still more 

 external nucleus lenticularis. The hippocampus similarly 

 indents the medial wall of the descending cornu, and follows 

 it in its backward and downward course. It is accompanied 

 by the posterior pillars of the fornix. These pillars are 

 approximated at the mesial end of the hippocampus, and pass 

 forwards as the body of the fornix to diverge close to the 

 anterior commissure to form the anterior pillars which curve 

 round the anterior side of the foramen of Monro and are directed 

 backwards to the corpus mammillare. 



Architecturally, the cerebrum is fundamentally that of the 

 lower vertebrate. It is an expansion of, and continuous with, 

 the forebrain and with the rest of the nervous system. But 

 the cerebrum of the mammal is much larger actually and 



