408 



GENERAL STRUCTURE AND FUNCTIONS 



in man, of about 100 mmm. They consist each of a central, trans- 

 parent, gelatinous mass, surrounded by an envelope of connective 

 tissue, which is marked by many tranverse elongated nuclei. Each 

 corpuscle receives one or two nerve fibres which run upward, in either 

 a straight or spiral course, and, after losing their medullary layer, in 

 some instances reach the central gelatinous nucleus, though for the 

 most part their terminations are not distinctly visible. 



The simplest form of tactile corpuscle is that known as the "terminal 

 bulbs" of the sensitive nerves, in the conjunctiva, the lips, the papillae 

 of the tongue, and the soft palate. They are round or elongated ovoid 

 bodies, consisting of a closed sac of connective tissue, sometimes marked 

 with transverse nuclei, and containing a homogeneous or finely granular 

 substance. Into this body is received the ultimate branch of a nerve 



Fig. 139. 



Fig. 140. 



TERMINAL BULB of a sensi- 

 tive nerve; from the conjunctiva 

 of the calf. (Frey.) 



TACTILE CORPUSCLES, from the edge of the 

 tongue of the sparrow. 1, 2. 3. IWedullated nerve 

 fibres supplying four tactile corpuscles. One 

 fibre divides into two branches; and one of them 

 is traced to near the extremity of the correspond- 

 ing corpuscle, where it ends in a cell-like expan- 

 sion. (Ihlder.) 



fibre, which is reduced to its axis cylinder and terminates in the inte- 

 rior by a free extremity. In some regions, as, for example, the lips in 

 the human subject, and the tongue in birds, are to be seen structures 

 which are intermediate in form between the terminal bulbs and the 

 tactile corpuscles. 



In the muscles, as a rule, each muscular fibre has, connected with it, 

 at least one nerve fibre, and sometimes more than one. The ultimate 



