S36 TEXT-BOOK OF PHYSIOLOGY 



The Nerve-cells. The nerve-cells of the cord are very numerous 

 and present a variety of shapes and sizes in different regions. They are 

 usually arranged in groups which extend for some distance up and down 

 the gray matter, forming columns more or less continuous 



Throughout the gray matter generally, in the ventral horns, in the 

 dorsal horns and in the intermediate portions as well, there are cells, the 

 axons of which pass into the immediately surrounding white matter of 

 the corresponding side, after which they divide into two branches, one of 

 which passes upward, the other downward, for a variable distance, and 

 finally reenter the gray matter at different levels. 



\t the base of the dorsal horn and on its inner side there is a well 

 marked group of cells which extends from the seventh or eighth cervical 

 nerves downward to the second or third lumbar nerves, being most promi- 



FIG. 224. DIAGRAM SHOWING LOCATION OF DIFFERENT GROUPS OF NERVE-CELLS IN THE 

 GRAY MATTER OF THE SPINAL CORD, i, Intrinsic cells, the axons of which pass into the 

 immediately surrounding white matter; 2, receptive or tract cells, the axons of which pass 

 into the white matter on the dorso-lateral and the ventro-lateral aspects of the cord; 3, emissive 

 or motor cells, which give origin to axons which become the ventral roots of the spinal nerves. 



nent in the thoracic region (Fig. 224). This column is known as Clarke's 

 vesicular column. From the nerve-cells constituting this column axons 

 pass obliquely outward into the more superficial portion of the white matter 

 on the lateral aspect of the cord when they turn upward and pursue a vertical 

 direction. Other groups of nerve-cells in the gray matter of the dorsal 

 horn send their axons across the median plane into the white matter in 

 the lateral and ventral regions after which they turn upward and pursue 

 a vertical direction. In the dorsal horn there are also cells which give 

 off axons which become related to cells in the ventral horns at the same 

 level and by means of collateral branches, with cells in the ventral horns 

 situated at higher or lower levels. These cells are termed correlation 

 cells or neurons. ^ (See page 115.) Some of the nerve-cells, their situation 

 and the distribution of their axons are shown in Fig. 224. 



