150 



COMPARATIVE ANATOMY. 



Other bands of nerve-fibres connecting parts of the brain 

 are spoken of as peduncles of the cerebellum (crura medullaa ad 

 cerebellum, crura cerebelli ad pontem, and crura cerebelli ad 

 corpora bigemina) and cerebrum (crura cerebri) (Fig. 125). 



In Mammals the mid-brain is of smaller relative size than in 

 other Vertebrates (Fig. 123, Mil]. A transverse furrow across its 

 dorsal surface divides it into four lobes (corpora bigemina). 



FIG. 126. CASTS <IF THK ]'I;AIX-('ASE.S OF EOCENE MAMMALS. (After Marsh.) 



Skull, with brain indicated, of A, Tillotherium fodiens ; B, Brontotherium ingens ; 

 C, Corj'phodon hamatus ; D, Dinoceras mirabile. K and F, ventral and lateral 

 views of casts of the brain of Dinoceras mirabile. 



The pineal gland (Fig. 123, Z] is displaced by the enlarged 

 hemispheres, and rests upon the anterior lobes. 



The reader is referred to Fig. 123 for details as to the relations 

 of the corpus callosum, the fornix, the thalamencephalon, the 

 three commissures of the central portion of the brain, &c. These 

 parts will be better understood by a comparison with the descrip- 

 tion of their development given in the introduction to this chapter. 



