300 MANUAL OF HISTOLOGY. 



nucleus, and a round nucleolus. These cells are polyhedral in 

 form, as is shown by the fact that sections made in all direc- 

 tions give them the same pyramidal or polygonal outline. In 

 nearly all the large cells there is in some part of the body an 

 aggregation of granules, which are often distinctly pigmented, 

 giving the appearance of a heap. 



Striations of the body have been frequently described and 

 depicted (Schultze, Schmidt, etc.), and this appearance has 

 been attributed by some to plications of a very delicate invest- 

 ing membrane, by others to ex- 

 pansions of the ultimate nervous 

 fibrillse, of which the axis-cyl- 

 inder was thought to be com- 

 posed. The motor cells average 

 about 40 fji. in diameter. The 

 cell -processes vary in number. 

 Most of them are bifurcating. 

 One, however, connected with 

 nearly every cell, can be fol- 

 lowed for a long distance with- 

 out dividing, and when the cell 

 is situated near the anterior 



FIG. 126. Diagram of a motor-cell from the 



anterior horn of a human cord in the cervical rOOtletS this prOCeSS lomS them 

 enlargement, x 800. J 



and acquires a myelinic sheath. 



This is called the axis-cylinder process. The branching pro- 

 cesses are called the protoplasmic processes, and are supposed 

 by some to freely anastomose with those of other cells. This 

 anastomosis, if it exist at all, is very delicate, and difficult of 

 demonstration. 



A certain number of the cells of the anterior horns, espe- 

 cially those located in the lateral region of the cornua, present 

 an elongated, fusiform aspect, and appear to have but two 

 processes. The nerve-cells in the posterior horns are of an 

 elongated oval or fusiform shape, their long diameter corre- 

 sponding in direction with that of the posterior horn. They are 

 very much smaller than the anterior cells, and less numerous. 

 Their average diameter is about 15 p,. They are seldom seen 

 to have processes. 



The myelinic nerve-fibres of the gray matter are seen prin- 

 cipally in the anterior horns, and converging from the cell- 

 groups to form the anterior root-radicles. Here and there fibres 



