240 



PHYSIOLOGY. 



out again to supply certain muscles of the neck and 

 shoulders. 



12. The last pair of cranial nerves, the twelfth, arise 

 near the middle line of the spinal bulb. This pair supply 

 the muscles of the tongue, and are called the hypoglossal 

 nerves. 



Brain composed of Two Hemispheres. It will be 

 observed that the brain, like the spinal cord, consists of 

 two lateral parts. Cutting sections of the brain length- 

 wise and crosswise shows that the outer part is made up 

 of gray matter and the inner part of white matter. The 

 gray matter is composed of cells essentially similar to those 

 of the spinal cord, while the white 

 matter of the inner part is composed 

 of white fibers like those of the outer 

 part of the spinal cord, or like the 

 nerves. 



Brain Convolutions and Intelli- 



79. Pyramidal Nerve gence. The brain of the rabbit has 

 i convolutions than that of the 

 cat, and is nearly smooth. In gen- 

 eral, the lower animals have fewer convolutions, and the 

 lower races of mankind have smoother brains than the 

 higher races. In the earlier stages of development man's 

 brain is smoother, but with growth the convolutions 

 appear, and increase in number with the growth of the 

 brain. As we know that intelligent action depends on 

 the gray matter of the surface of the brain, we infer that 

 to accommodate its increase in the brain case it is thrown 

 into folds, as the surface of the lining of the intestines is 

 increased by folds and villi. 



