ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. (>15 



in the form of amorphous matter. The only connective tissue pres- 

 ent in the cord is carried in by the blood-vessels. 



GRAY MATTER OF THE COHU. The gray substance of the cord 

 is composed of neuroglia, fibrils, and nerve-cells. 



The cells of the cord are formed by a small mass of protoplasm 

 in which is plunged a nucleus surrounded by pigment-granules. 

 These cells, whose volume varies with the groups, have a certain 

 number of prolongations. 



Cell-arrangement. The cells of the cord are not disseminated 

 in the gray substance in a disorderly way. They are grouped at cer- 

 tain points to form nuclei nuclei of nerves; these are situated one 

 above the other in a fashion to form columns parallel with the long 

 axis of the cord. 



There are distinguished three groups in the anterior liorns: an 

 interior internal group, an anterior external group, and a posterior 

 external group. 



In the posterior horns the cells are fewer in number; it is only 

 at the internal part of the neck of these horns that there is found a 

 groupie g. It is known as the dorsal nucleus of Stilling or the vesi- 

 cular column of Clarke. 



The ganglionic cells of the anterior horns are very large, star- 

 shaped, and from 1 / 3 - to 1 / 200 inch in diameter. That is, they are 

 nearly large enough to be visible to the naked eye. 



Degeneration. The nuclei of origin of the anterior roots are 

 seized with degeneration in the various forms of muscular atrophy. 

 The cells, by reason of their function, are known as motor cells. They 

 are motors for the muscles to which their nerves go, and trophic for 

 the same nerves and muscles. Progressive muscular atrophy is ana- 

 tomically characterized by a general atrophy of the motor cells of the 

 anterior horns of the cord. Children's palsy is also characterized by 

 atrophy of these cells. 



The cells of the posterior horns, irregularly distributed in the 

 neuroglia, are fewer in number and smaller in size than are those of 

 the anterior horns. Their diameters average about Vi 2 oo i ncn - 



Anatomically, the column of Clarke exists only from the second 

 lumbar to the eighth dorsal pair of nerves. However, there are small, 

 erratic groups of cells and two restiform nuclei at the level of the 

 medulla which are analogous to the two columns of Clarke. The cells 

 of the column of Clarke are very large, star-shaped, and only very 



rgerly branched. 

 The intermedio-lateral gray column is in the outermost portion of 



