THE NERVOUS SYSTEM. 195 
ram communicantes, join the adjacent ganglion of the 
sympathetic cord (Fig. 107). Each of the four branches 
contains both motor and sensory fibers, or, in other words, 
fibers from both roots. 
The exit and entrance of the nerve roots divide the white 
matter of the lateral half into three columns named, accord- 
ing to their location, the anterior column, the lateral column, 
and the posterior column. The first is ventral to the an- 
terior nerve roots, the last is dorsal to the posterior nerve 
roots, while the lateral column is between the roots. 
The elements of the spinal cord, like those of the brain, 
are of two kinds—the cells composing the gray matter and 
—— d 
Gal 
Fic. 100. D1AGRAMMATIC CROSS-SECTION OF THE SPINAL Corp. The cells 
and fibers are represented too few and too large in proportion to the 
size of the cord. * 
ag, Anterior horn or column of gray matter; a, nerve process of the cell 
¢; an, anterior root; cc, canalis centralis; c, one of many cells form- 
ing the ganglion on the posterior root; d, posterior fissure; e, cell 
giving off an axone into the anterior root; du, dorsal branch; 
f, cut-off fibers; gu, ganglion of posterior root; i, axone of the 
cell io; nc, junction of anterior and posterior roots; ps, posterior 
root of nerve; pg, posterior horn of gray matter; s, terminal arbor- 
ization of part of fiber from c; v, anterior median fissure; vn, ven- 
tral branch of nerve; van, axone of anterior horn cells; +, the part 
of the posterior root fiber extending caudad in the cord. 
the fibers composing the white matter. While in the brain 
the gray matter is largely on the surface, forming the 
cortex, in the cord it occupies the central region. A canal, 
