510 



HANDBOOK OF PHYSIOLOGY. 



the complexity and depth of the convolutions, which indicate the area of 

 the gray matter of the cortex, correspond 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 de- 

 scend 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 distinguish 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 



FIG. 351. 



FIG. 352. 



Fra. 351. Diagrammatic horizontal section of a Vertebrate brain. The figures serve both for 

 this and the next diagram. Mb, mid brain: what lies in front of this is the fore-, and what lies 

 behind, the hind-brain; Lt, lamina terminalis; Olf, olfactory lobes; Hmp, hemispheres; Th. E, 

 thalamencephalon; Pn, pineal gland; Py, pituitary body; F. M, foramen of Munro; cs, corpus 

 striatum; Th, optic thalamus; CO, crura cerebri: the mass lying above the canal represents the 

 the corpora quadrigemina; Cb, cerebellum: I IX., the nine pairs of cranial nerves; 1, olfactory 

 ventricle; 2, lateral ventricle; 3, third ventricle; 4, fourth ventricle; +, iter a tertio ad quartum 

 ventriculum. (Huxley.) 



FIG. 352. Longitudinal and vertical Diagrammatic section of a vertebrate brain. Letters as 

 before. Lamina terminalis is represented by the strong black line joining Pn and Py. (Huxley.) 



covering the cerebellum, (d.) The presence of posterior cornua in the 

 lateral ventricles. 



The most distinctive points in the human Irain, 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., which 

 is less than the weight of the human adult male brain, and barely ex- 

 ceeds that of the human infant at birth. (2.) The much greater com- 

 plexity of the convolutions, especially the existence in the human brain 



