THE NERVOUS SYSTEM 



227 



(Fig. 104). On the dorsal or sensory root is a small ganglion 

 located very near the junction of the two roots. The common 

 spinal nerve, formed by the union of the two roots, almost 

 immediately divides into four branches, one of which, the dor- 

 sal, supplies the muscles and skin along the vertebral column; 

 a second, the ventral branch, supplies the limbs or intercostal 

 spaces; while the other two branches, rami communicantes , 

 join the adjacent ganglion of the sympathetic cord (Fig. 118). 



Fig. III. — Diagrammatic Cross-section of the Spinal Cord. The cells 

 and fibers are represented too few and too large in proportion to the size of the 

 cord. 



ag, Ventral horn or column of gray matter; a, nerve process of the cell; c, 

 an, ventral root; cc, central canal; c, one of the cells forming the ganglion 

 on the dorsal root; d, dorsal median sulcus; e, cell giving off an axone into 

 the ventral root; dn, dorsal branch;/, cut-off fibers; gti, ganglion of dorsal root; 

 i, axone of the cell io; «c, junction of dorsal and ventral roots; /j^, dorsal root 

 of nerve; pg, dorsal column of gray matter; s, terminal arborization of part of 

 fiber from c; v, ventral median fissure; vn, ventral branch of nerve; van, axones 

 of ventral column cells; x, the part of the dorsal root fiber extending craniad in 

 the cord. 



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 w^hite 

 matter of the lateral half into three columns named, according 

 to their location, the ventral column, the lateral column, and the 

 dorsal column. The first is ventral to the ventral nerve roots, 

 the last is dorsal to the dorsal nerve roots, while the lateral 

 column is between the roots. 



