384 DEVELOPMENT OF OKGANS IN MAMMALIA. [CHAP. 



Primitively the Mammalian cerebrum, like that of 

 the lower Vertebrata, is quite smooth. In some of the 

 Mammalia, Monotremata, Insectivora, etc., this condition 

 is retained nearly throughout life, while in the majority of 

 Mammalia a more or less complicated system of fissures 



LATERAL VIEW OF THE BRAIN OF A CALF EMBRYO OF 5 CM. 

 (After Mihalkovics.) 



The outer wall of the hemisphere is removed, so as to give a 

 view of the interior of the left lateral ventricle. 



hs. cut wall of hemisphere ; st. corpus striatum ; am. hippo- 

 campus major (cornu ammonis) ; d. choroid plexus of lateral 

 ventricle ; fm. foramen of Monro ; op. optic tract ; in. in- 

 fundibulum ; mb. mid-brain ; cb. cerebellum ; IV. V. roof of 

 fourth ventricle ; ps. pons Varolii, close to which is the fifth 

 nerve with Gasserian ganglion. 



is developed on the surface. The most important, and 

 first formed, of these is the Sylvian fissure. It arises at 

 the time when the hemispheres, owing to their growth 

 in front of and behind the corpora striata have assumed 

 somewhat the form of a bean. At the root of the 

 hemispheres the hilus of the bean there is formed a 



