124 



PERIPHERAL NERVE TERMINATIONS 



FIG. 119. TACTILE CELLS IN THE EPITHELIUM OF 

 THE GROIN OF A GUINEA-PIG. 



a, tactile cell ; c, epithelial cell ; m, tactile men- 

 iscus, at the end of a nerve fibril; w, nerve fibre. 

 Chlorid of gold. Highly magnified. (After Ean- 

 vier.) 



which are in contact with the surface, but rarely, if ever, pene- 

 trate the interior of the epithelial cells. The " trefoil plates " of 

 Bethe represent unusually large end knobs. 



II. TACTILE CELLS (Merkel). These are modified epithelial 

 cells, with clear cytoplasm and a slightly vesicular nucleus, which 



are found in the deeper 

 layers of the stratified epi- 

 thelium of the epidermis 

 and in the root sheaths 

 of hairs. These cells are 

 recognized by their vesicu- 

 lar character and by the 

 fact that they occur most 

 abundantly in the inter- 

 papillary portions of the 

 epidermis. The deeper 



,1 , . n -,, 



surface of the tactile cell 

 rests in a cup-like expan- 

 sion of a terminal nerve 

 fibril which is known as 

 the tactile meniscus. 



III. NETTRO-EPITHELITTM. The cells of some types of neuro- 

 epithelium, e. g., the olfactory cells, are true nerve cells ; others 

 are modified epithelial cells, in relation to which the nerves termi- 

 nate by intercellular end fibrils. The neuro-epithelium of the eye 

 and the ear will be described in the chapters devoted to these 

 organs, that of the gustatory organ forms typical nerve end 

 organs, the taste buds. 



IV. TASTE BUDS (gustatory organ). These end organs ap- 

 pear to be concerned with the special sense of taste. They occur 

 in the stratified epithelium of the base of the tongue, uvula, soft 

 palate, and epiglottis. Disse has also found similar structures 

 in the nasal mucous membrane. They are most abundant on the 

 lateral surfaces of the circumvallate papillae of the tongue and 

 on the walls of the sulci in the foliate papillae which are most 

 highly developed in the rabbit. They are occasionally found on 

 the fungiform papillae of the tongue, where they occur in consid- 

 erable numbers in fetal life but mostly disappear before birth, and 

 in the lateral walls of the sulci about the circumvallate papillae. 



Taste buds are ovoid, ellipsoidal, or spheroidal masses which 

 occupy almost the entire depth of the epithelial layer. Their 



