THE NERVOUS SYSTEM. 



625 



convolutions, which indicate the area of the gray matter of the cortex, corre- 

 spond with the degree of intelligence. 



Weight of the Spinal Cord. The spinal cord of man weighs from 1 1 oz. ; 

 its weight relatively to the brain is about 1:36. As we descend the scale, 

 this ratio constantly increases till in the mouse it is 1 : 4. In cold-blooded 

 animals the relation is reversed, the spinal cord is the heavier and the more 

 important organ. In the newt, 2:1; and in the lamprey, 75 : 1. 



Distinctive Characters of the Human Brain. The following characters dis- 

 tinguish the brain of man and apes from those of all other animals, (a.) The 

 rudimentary condition of the olfactory lobes, (b. ) A perfectly defined fissure 

 of Sylvius, (c. ) A posterior lobe completely covering the cerebellum, (d. ) 

 The presence of posterior cornua in the lateral ventricles. 



The most distinctive points in the human brain, as contrasted with that of 

 apes, are: (1.) The much greater size and weight of the whole brain. The 

 brain of a full-grown gorilla weighs only about 15 oz. (450 grms.), which is 

 less than | the weight of the human adult male brain, and barely exceeds that 

 of the human infant at birth. (2. ) The much greater complexity of the con- 

 volutions, especially the existence in the human brain of tertiary convolutions 



CJt 



Fig. 377. -Brain of the Orang, % natural size, showing the arrangement of the convolutions. 

 S-y, fissure of Sylvius; R, fissure of Rolando; EP, external perpendicular fissure; Olf, olfactory 

 lobe; 06, cerebellum; PF, 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. (Gratiolet.) 



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 (rostrum) 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 up- 

 ward. (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. 



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



of the Qrang. 



4 



