TISSUES. 95 



They have one or more processes, no cell wall, and a 

 distinct nucleus. The nucleus has a conspicuous 

 nucleolus, a prominent nuclear membrane, but a 

 small supply of chromatin. 



The cytoplasm is usually pigmented, the pigment 

 being collected to one side of the cell. It is this 

 pigment that gives nervous tissue a gray color 

 wherever these cells are found. Fat and vacuoles 

 are also usually found in the cytoplasm. The proc- 

 esses of nerve cells are : 



Fibrils o! axial 

 cord. 



Medullary 

 sheath. 



Fig. 61. Transverse section through the sciatic nerve of a frog. 

 At a and b is a diagonal fissure between two Lantermann's segments; 

 as a result, the medullary sheath here appears double (Bohm and 

 Davidoff). 



I. Axis cylinder (Deiters' process, axon, neurite, 

 or neuraxon), which is usually a long protoplasmic 

 process that physiologically carries an impulse away 

 from the cell. Collaterals are nerve processes that 

 leave the axis cylinder at right angles. They are 

 commonly found near the nerve cells, but may ap- 

 pear at a node of Ranvier some distance away from 

 the nerve cell. 



