224 



HUMAN PHYSIOLOGY 



CHAP. 



course. Some nerves are very short 

 and so small that they can scarcely 

 be seen with the naked eye. 



If a nerve is cut across and exam- 

 ined under the microscope, it will 

 be seen to consist of many very 

 fine nerve threads or fibers, held to- 



FlG. 119. A section of a frog's nerve, showing 

 the sheath and nerve fibers. 



gether by fatty connective tissue and 

 the whole surrounded by a sheath. 

 Each fiber is an outgrowth of a 

 nerve cell, an axone or a dendrite, 

 and runs to its destination unbroken 

 like a single continuous wire of a 

 large cable. A large nerve has 

 thousands of separate fibers. 



I 



-Node 



FIG. 120. Showing A, a nerve cell with all its parts dendrites, cell body, and 

 axone; and B, a portion of a nerve fiber, highly magnified. (Drawn by Pratt.) 



