IO2 



HISTOLOGY. 



c.t. 



FlG. 119. NON-MEDULLATED NERVES, 



FROM A CAT'S INTESTINE. 



A, From the submucous and B, from 

 the myenteric plexus, c. t., Con- 

 nective tissue; n., sympathetic, 

 non-medulla ted nerve fibers; n. c., 

 nerve cell; s. m., smooth muscle. 



medullated nerves are shown in Fig. 119; A represents a nerve which 

 is easily recognized by the two large nerve cells which it contains; B 

 is a bundle of fine fibers containing a few nuclei, probably of connective 

 tissue. 



The recognition of small nerves in ordinary sections may be facilitated 

 by remembering that they are fibrous bundles extending through con- 

 nective tissue and found in the same situa- 

 tions as the vessels. The latter are tubes 

 lined with eridothelium. Sometimes they are 

 filled with corpuscles (Fig. 118) but the cor- 

 puscles never appear fibrous and usually 

 stain unlike anything else in the specimen. 

 Xerves differ in texture from the white fiber 

 of connective tissue, which forms a diffuse 

 network or layer instead of occasional dis- 

 tinct circumscribed bundles. 



SENSORY ENDINGS. The way has al- 

 ready been described, in which ectodermal 

 cells become detached from the medullary 

 tube to form spinal and cerebral ganglia, afterwards becoming bipolar and 

 then T-shaped, sending a long dendrite through the nerve bundle to the 

 periphery. Soon after it leaves the cell body, this process becomes sur- 

 rounded by the neurolemma and myelin sheath. Its branches are very few 

 until it nears its distal end when it forks repeatedly at the nodes. Finally 

 it loses its sheaths and is resolved into many small fibers which terminate 

 in contact with epithelial, connective tissue or muscle cells. These terminal 

 branches of the dorsal root fibers are the sensory nerve 



j j_.^ 



endings. Apart from those of -the special sense organs, 

 to be described with the eye, ear, etc., they are as fol- 

 lows. 



Free nerve endings. Sensory nerves to the epi- 

 thelia, such as the epidermis, or that which forms part 

 of the mucous membrane of the mouth, or the corneal 

 epithelium, lose their myelin sheaths and divide repeat- 

 edly in the connective tissue just beneath. The un- 

 sheathed slender fibers thus formed pass between the 

 epithelial cells where they ramify further, and terminate with pointed or 

 club-shaped ends (Fig. 120). Such free endings are too delicate to be seen 

 in ordinary preparations. Sometimes the terminal fibers in the lower 

 layers of the epidermis expand into crescentic structures called tactile 

 menisci (Fig. 121). An epidermal cell, the base of which rests upon a 



FIG. 120. FREE NERVE 

 ENDING, IN EPI- 

 THELIUM. GOLGI 

 PREPARATION. 



(After Retzius.) 



