ARRANGEMENT OF THE NER VE FIBRES. 2 1 1 



here between 600 and 1,400 examples. They may occur 

 manifold or isolated. 



In mammals we meet with them in the sole of the foot. 

 An admirable locality is the mesentery of the cat. Many of 

 the latter animals contain them in innumerable quantities ; in 

 others, on the contrary, one may bother and fret one's self and 

 find only 6 to 12 altogether. 



The capsular system of the Pacinian corpuscle {b) is much 

 more complicated in its structure than the simple envelope 

 of the terminal bulb. 



It consists of a considerable number of thin, connective- 

 tissue membranes, embedded over each other, and kept tense 

 by a fluid intermediate substance. They formerly appeared 

 to contain nuclei in their parietes. According to the investi- 

 gation of Hoyer, however, their inner surfaces are lined by 

 a thin covering of nucleated endothelial cells. The outer 

 capsular systems are further removed from each other, follow- 

 ing the curvature of the entire structure ; the inner ones are 

 more nearly approached to each other, their lateral curvature 

 is lessened, and they finally surround an axial canal. This, 

 the so-called inner bulb (c), may be compared to the Krause's 

 corpuscle. It is filled by a homogeneous, tolerably resistant 

 substance. 



The capsular systems unite below, and form a thicker con- 

 nective-tissue tube (a). Through it passes a broad or medium 

 sized, but always double contoured nerve fibre. Having 

 entered the inner bulb, it loses (at c, below) the medullary 

 sheath ; it becomes an axis cylinder, and terminates towards 

 the upper closed pole, for the most part undivided, occasion- 

 ally (and then varying in its details) divided (c, above). This 

 axis cylinder is the most beautiful known. It shows a longi- 

 tudinally striated structure, and consists of primitive fibrillae. 



Let us turn, finally, to the so-called tactile bodies of the 

 human integument (Fig. 183). They belong — no doubt can 

 prevail concerning this — to the related series of the terminal 

 bulbs and Pacinian structures ; but the nerve termination is 

 not yet known. 



