52 AGE, GROWTH, AND DEATH 



microscopic structure the same supporting role which 

 the skeleton performs in the gross anatomy of the 

 body as a whole. They do not take an active part 

 in the nervous functions proper. None of the ap- 

 pearances which this figure offers for our considera- 

 tion can be recognised in any similar preparation of 

 the embryonic cord. Obviously, then, from the em- 

 bryonic to the adult state in the spinal cord there 

 occurs a great differentiation. That which was alike 

 in all its parts has been so changed that we can readily 

 see that it consists of many different parts. A strik- 

 ing illustration of this is afforded by the next picture, 

 which represents one of the large nerve cells which 

 occur in the small brain, or cerebellum, that portion 

 of the central nervous system which the physiologists 

 have demonstrated to be particularly concerned in the 

 regulation and co-ordination of movements. These 

 large cells occur only in this portion of the brain, and 

 as you see, differ greatly in appearance from the 

 motor cells of the type which we were considering a 

 few moments ago. And, again, another picture illus- 

 trates yet other peculiarities of the adult nerve cells. 

 The upper figures in this plate are taken from cells 

 which have been coloured uniformly of a very dark 

 hue, in consequence of which they are rendered so 

 opaque that the nucleus which they really contain is 

 hidden from our view. But the deep artificial colour 

 makes it easy to follow out the form of the cells and 

 the ramifications of their long processes. In the 

 middle figures we have cells which have been stained 



