OF THE NERVOUS SYSTEM. 



413 



covers its normal sensibility. Restoration may also undoubtedly take 

 place in nerves of larger size, as in the case reported by L'EtieVant, 1 

 where the median nerve was divided in a man twenty-six years of age, 

 at the upper third of the arm. The power of motion and sensibility, 

 dependent on the fibres of this nerve, remained abolished for ten 

 months, but began to reappear in fourteen months, and were almost 

 completely restored at the end of a year and a half. 



Nerve Cells, 



The nerve cells, which form the characteristic anatomical element of 

 the gray substance, are rounded or irregularly shaped bodies, consisting 

 of a soft, semi-transparent, finely granular, albuminous matter, and con- 

 taining a rather large, distinctly marked nucleus and nucleolus. Some- 

 times they also contain a certain quantity of brown, yellowish, or 

 blackish pigment grains, which are especially abundant in the imme- 

 diate neighborhood of the nucleus. The nerve cells vary in size in dif- 

 ferent parts of the gray substance. The smaller ones, from 10 to 20 

 mmm. in diameter, are found in the ganglia of the sympathetic system, 

 the convolutions of the cerebral hemispheres, and in the posterior horns 

 of gray matter in the spinal cord. The larger, averaging from 40 to 60 

 mmm., are in the convolutions of the cerebellum, and in the medulla 

 oblongata ; the largest of all, as a general rule, being met with in the 

 anterior horns of gray mat- 

 ter of the spinal cord, where 

 they reach the diameter of 

 130 or 135 mmm., or seven- 

 teen times the size of the red 

 globules of the blood. 



The most marked anato- 

 mical features of the nerve 

 cells are their prolonga- 

 tions. These are narrow 

 processes or extensions of 

 the cell substance, and con- 

 sisting apparently of the 

 same material. In the gan- 

 glia of the sympathetic sys- 

 tem, and in those situated 

 upon the roots of the spinal 

 and cranial nerves in man, 

 the nerve cells have for the 

 most part a rounded form, 

 and only one or two pro- 

 longations. Throughout the 

 gray substance of the braiu 



Fig. 142. 



**" 



' "" 



Trait6 des Sections Nerveuses, p. 54. 



