THE NERVE FIBER 



101 



only one or two main dendrites which subdivide to form a thick 

 bush-Uke thicket of processes. An axon arising from the base of 

 the cell body extends into the white matter. 



Motor neurons of the spinal cord have irregularly stellate shapes 

 due to the origin of dendrites from many points. (Fig. 56.) The 

 axon is a single, slender, and smooth process of the cell bod\' 

 and often extending long distances. 



Craniospinal ganglion cells have a superficial appearance of 

 unipolar conditions. The cell body is globular or pyriform, and 

 has a single process which has the characteristics of an axon. Em- 

 bryologically the cells produce two processes, a bipolar condition, 

 but later the processes fuse in a common outlet. This single process 

 usually branches to form two axon-like processes, one extending to 

 the periphery, regarded as a dendrite, and the other passing into 

 the dorsal horn of gray matter of the cord and regarded as an 

 axon. Surrounding each of the ganglion cells is a sheath of smaller 

 satellite cells, or cells of Schwann, since they are believed to con- 

 tinue out over the process to become continuous with the sheath of 

 Schwann covering the fiber. (Fig. 52.) 



THE NERVE FIBER. 



As the axons of neurons pass into the white matter from the gray 

 matter of the cerebrum, cerebellum, and spinal cord, they are clothed 



Fig. 57. — Cross-sections of myelinated peripheral nerves, showing appearance 

 following different treatments. A, fixed in Bouin; stained in eosin and hematoxylin. 

 The myelin is dissolved away. B, prepared with silver impregnation to show the 

 axis cylinder. C, fixed with osmium tetroxide and preserving the myelin. 



with a lipoid substance, called myelin. (Fig. 57.) As myelinated axons 

 pass from the brain an'd cord to become the components of cranial 

 and spinal nerves, a sheath of Schwann, or neurolemma sheath, is 

 added. This consists of a successive series of flat, nucleated cells 



