FUNCTIONAL PARTS OF THE NERVOUS SYSTEM 



63 



FIG. 32 



the different parts of these can exert on the brain all degrees of local or 

 general pressure, as normal function demands. Osmosis may have much 

 to .do with these adaptive movements of liquid. Only few details, how- 

 ever, of these vasomotor activities have so far been obtained, but there is 

 little doubt that the conditions are complex and important. Perhaps the 

 pituitary body has chemical control over the blood-supply of the brain, 

 for it seems to contain a vasoconstrictor principle thirty times as strong 

 as adrenalin. (See Chapter on 

 Nutrition.) The reciprocal vaso- 

 motor action between the trunk 

 and limbs and the blood-supply 

 of the head has long been a well- 

 known fact. 



Another function of this "water 

 jacket" of the brain is to protect 

 it from injury by blows on the 

 skull. The spinal cord is supplied 

 with blood by arterioles extending 

 inward from the pia mater. Cap- 

 illaries are especially abundant 

 about the nerve-cells, especially in 

 the cortex cerebri. The imme- 

 diate dependence of the brain's 

 function on ample and continuous 

 blood -supply is the most com- 

 plete found in the body. When 

 the flow of blood ceases or even 

 slows greatly the central functions 

 cease. Illustrations of this fact 

 are seen in the instant dropping 

 dead of people when the heart 

 stops beating or bursts. 



CO 



Diagrammatic suggestion of an arachnoidal 

 villus and its coverings: co, gray cortex of the 

 hemisphere; p, pia intima; aa, subarachnoidal 

 space continuous with the villus, pa; a, arachnoid; 

 sd, subdural space, continuous with that of the 

 villus, sd f ; d, inner layer of the dura mater sep- 

 arated from the upper layer, (d / ) by the venous 

 space, v; ds, dural covering of the arachnoidal 

 villus. (Rauber.) 



FUNCTIONAL PARTS OF THE NERVOUS SYSTEM. 



Certain portions of the nervous system should be especially studied 

 because of their diagnostic importance if for no other reason, though little 

 is known about some of them. We will consider briefly the uses of the 

 hemispheres (including their much-discussed cortex), the cerebellum, 

 the medulla oblongata, the optic thalami, the corpora striata, and the 

 pons. 



The Hemispheres. The hemispheres, or cerebrum, as they are some- 

 times called, are the large convoluted, seamed masses of white protoplasm 

 which are seen in the opened skull when the tough dura mater and the 

 thin arachnoid and pia mater ("meninges" of the brain) have been cut 

 through. The hemispheres in man cover over all the remainder of the 



