THE CEREBRO-SPDSTAL NERVOUS SYSTEM. 



511 



of tertiary convolutions in the sides of the fissures. (3.) The greater 

 relative size and complexity, and the blunted quadrangular contour of 

 the frontal lobes in man, which are relatively both broader, longer, and 

 higher, than in apes. In apes the frontal lobes project keel-like (ros- 

 trum) between the olfactory bulbs. (4.) The much greater prominence 

 of the temporo-sphenoidal lobes in apes. (5.) The fissure of Sylvius is 

 nearly horizontal in man, while in apes it slants considerably upwards. 

 (6.) The distinctness of the external perpendicular fissure, which in apes 

 is a well-defined almost vertical "slash," while in man it is almost 

 obscured by the annectent gyri. 



Fio. 353. Brain of the Orang, % natural size, showing the arrangement of the convolutions. 

 Sy, fissure of Sylvius: R, fissure of Rolando; E P, external perpendicular fissure: Olf, olfactory 

 lobe; C 6, cerebellum; P V, pons Varolii; M O, medulla oblongata As contrasted with the human 

 brain, the frontal lobe is short and small relatively, the fissure of Sylvius is oblique, the temporo- 

 sphenoidal lobe very prominent, and the external perpendicular fissure very well marked. (Gratio- 

 let.) 



Most of the above points are shown in the accompanying figure of the 

 brain of the Oraug. 



Functions of the Cerebrum. 



Speaking in the most general way, and for the present omitting the 

 accumulating evidence in favor of the direct representation of the vari- 

 ous co-ordinated movements of the muscles of the body in ganglia situ- 

 ated in different parts of the cerebral cortex, it may be said that: (1.) 

 The Cerebral hemispheres are the organs by which are perceived those 

 clear and more impressive sensations which can be retained, and regard- 

 ing which we can judge. (2.) The Cerebrum is the organ of the will, in 

 so far at least as each act of the will requires a deliberate, however quick 

 determination. (3. ) It is the means of retaining impressions of sensible 

 things, and reproducing them in subjective sensations and ideas. (4.) 

 It is the medium of all the higher emotions and feelings, and of the 



