NERVOUS TISSUE 



157 



the medullary sheaths of the spinal nerves are not all formed until two or three years 

 after birth. They continue to increase in thickness into adult life. 



NERVE ENDINGS. 



SENSORY ENDINGS. The outward growth of nerve fibers from cells 

 in the ganglia of the spinal and cerebral nerves has already been described. 

 Near their terminations these fibers branch repeatedly at the nodes, lose 

 their myelin sheaths, and form terminal arboriza- 

 tions in contact with epithelial, connective tissue, or 

 muscle cells. These are the sensory endings, and 

 apart from those connected with the eye, ear, and 

 other organs of special sense, they may be described 

 as follows. 



Free Endings. Sensory fibers to the epidermis 

 and to the corneal and oral epithelia penetrate the 

 basal layer, passing between the cells as unsheathed 

 fibers, and ramify among the cells in the outer layers 

 (Fig. 145). The extremities of the fibers, which may be pointed or 

 club-shaped, are in contact with the epithelial cells, but do not enter 

 them. In the process of branching the neurofibrils become distributed 



FIG. 145. FREE NERVE 

 ENDING, IN EPITHE- 

 LIUM. GOLGI PREP- 

 A R A T i o N . (After 

 Retzius.) 



Intraepithelial 

 fiber. 



Papilla 



Capillaries. 



Tactile cells. 



meniscus. 



Corium. 



FIG. 146. 



Tactile cells Nerve fiber, 



in the corium. 



FIG. 147. 



FIGS. 146 AND 147. FROM VERTICAL SECTIONS THROUGH THE SKIN OF THE GREAT TOE FROM A MAN OF 



TWENTY-FIVE YEARS. X 360. 



in smaller and smaller bundles, which often anastomose, forming plexuses; 

 but whether the interlacing constituent fibrils unite with one another so 

 as to form a net has been questioned. At the ends of the branches, each 



