148 



HISTOLOGY 



nerves. Connective tissue, containing small blood vessels, passes be- 

 tween the ensheathed cells of the ganglion. 



In the embryo the cells of the spinal ganglia are bipolar, but generally 

 they become unipolar, with T-shaped processes, as already described. 

 In the ganglia of the acoustic nerve, however, the bipolar form is said to 

 be retained, and these cells are not surrounded by capsule or "mantle" 

 cells. In other ganglia of the cerebral nerves, and in spinal ganglia, the 

 cells are arranged as shown in the diagram, Fig. 135. Their branches 

 can be studied only in special preparations, made usually by 

 Ehrlich's methylene blue method, or CajaPs silver nitrate method. 



Cross section of a medullated nerve fiber. 

 I 



Nucleus of the 

 capsule 



~~ Protoplasm. 



Longitudinal view 

 of medullated 

 nerve fibers. Surface view of 



nucleated sheath. 



FIG. 134. FROM A CROSS SECTION OF A HUMAN SEMILUNAR GANGLION. X 240. 



At x the beginning of a protoplasmic process has been included in the section; elsewhere the processes 



cannot be seen. 



The most characteristic cells (Fig. 135, 3) have large round bodies 

 and a single spirally coiled process, which arises from a conical 

 projection of the protoplasm. The process often winds about the 

 cell body. Soon after passing through the capsule it acquires a sheath 

 of myelin, and is covered with neurolemma. It may give off collaterals be- 

 fore it divides into its two main branches, which correspond with dendrite 

 and neuraxon respectively. Sometimes the process divides into three 

 branches (Fig. 135, 2); the branching takes place at a node of Ranvier. 

 Certain of the large cells, as found constantly in the human jugular gang- 

 lion, lack the coiled windings, so that the process passes directly through 

 the capsule and divides at once into its two branches. 



Frequently the ganglion cells are provided with short processes which 

 end in rounded enlargements, either within the capsule (Fig. 135, 5) or 

 outside of it (Fig. 135, 6). Collateral branches may end in this way. 



