222 



ANATOMY OF THE CENTHAL NEEVOUS SYSTEM. 



fissure^ in order to facilitate the comparison with the human brain. The 

 frontal lobe, lying in front of it, is seen to be very much less developed than 

 i]i Pig. 130. It is diflficult to homologize the frontal sulci. The central 

 fissure runs more vertically, probably on account of the imperfect develop- 



Fig. 145.— Brain of a bear. The frontal lobe is shaded. (After Turner.) 



ment of the frontal lobe; likewise all the parts lying behind it are, in a 

 measure, pushed upward, the fissura Sylvii standing almost vertically. Ar- 

 cuate fissures surround the fissura Sylvii, on which, upon comparison with 

 Fig. 130, a similar arrangement is readily recognized after a moment's con- 



Fig. 146. — Brain of the narwhal: Monodon inonoceros. (After Turner.^ 



sideratioil: how these pass over into the temporal sulci and the interparietal 

 fissure. 



The Sylvian fissure is more vertical in all animal brains than in that of 

 man; it is more horizontal the more the frontal lobe is developed. It is 

 commonly relatively short. 



