204 ANATOMY AND PHYSIOLOGY FOR NURSES 



two roots from the anterior and posterior columns of 

 the spinal cord. The posterior roots are larger than the 

 anterior. The anterior are the motor radicles, and the 

 posterior, the sensory. 



On each of the posterior roots, in the openings between 

 the bones of the spinal column (intervertebral foramina), 



FIG. 105. Longitudinal nerve- 

 fiber (diagrammatic) : a, Axis- 

 cylinder ; b, medullary she ith ; c, 

 neurilemma ; d, nucleus ; a, node 

 of Ranvier (Leroy). 



Fibrils of axial 

 cord. 



Neurilemma. 



Segment of 

 Lantermann. 



FlG. 106. Longitudinal section 

 through a nerve-fiber from the sciatic 

 nerve of a frog (x 830) (Bohm and 

 Davidoff). 



a ganglion is formed, after which the anterior and posterior 

 roots of the nerve unite and form the spinal nerve. 



The ganglia may be considered as distinct centers, 

 giving off branches in different directions : the superior, or 

 ascending, to communicate with the ganglion above; the 

 inferior, or descending, to communicate with the ganglion 

 below ; the external, to communicate with the sympathetic 



