40 



ANATOMY OF THE OENTKAL NEETOUS SYSTEM. 



with in the periphery; they are similarly found in the vertebrates, and in 

 many different forms, as is the case in the nerve-endings of the sense-organs. 

 The epithelium of the nasal mucous membrane, like that of the angle- worm, 

 sends only one process back into the brain; but in the ear there are no 

 end-cells in this sense, the corresponding cells lying in the spinal ganglion 

 of the cochlea, while their branched peripheral processes surround the hair- 

 cells of the crista acustica, or of the organ of Corti, after the manner of 

 the sensory nerve with the epidermis-cell (Fig. 16). So also with the taste- 

 iibers has such a branching around cells been determined. In the retina, 

 we know, there are nerve-fibers which come from the brain and arborize 



Fig. 15. — a, Sensory epithelium of the earth-worm. 6, Sensory epithelium 

 of the snail, c, Spinal ganglion-cells of a vertebrate. (After Eetzius.) 



[One process of the cell (c) extends to the skin as a sensory nerve-fiber; 

 it is the homologue of the dendrite, but in this situation is structurally modified 

 into a typical axis-cylinder. One process extends into the central nervous sys- 

 tem, and is the efilerent neuraxon, axone, or neurite, also here having the structure 

 of a typical axis-cylinder. Such cells have been called bipolar, because they 

 possess two axis-cylinders; inasmuch, however, as they possess but one neuraxon, 

 the utility of the term bipolar might be called in question. — W. S. H.] 



around their respective cells, while there are also ganglion-cells in it, whose 

 axones pass backward into the brain. 



Sensory nerves are widely distributed over the entire body. They are 

 located not only in those places usually known to be sensitive, but also in all 

 other tissues and organs. '\^'hether one examine the liver or the kidney, the 



