350 THE NERVOUS SYSTEM. 



contain a fluid or semifluid interstitial substance, in which the terminal 

 nerve fibre is enclosed and in which it ends, either by expansion into 

 the so-called " terminal buds," or by the indefinite disappearance of its 

 fibriHa?. 



The Pacinian bodies of the hands and feet in man, and in correspond- 

 ing situations in many of the quadrupeds, are from 1 to 4.5 millimetres 

 in length. Their substance is enclosed in numerous concentric cap- 

 sules, each of which, according to Key and Retzius,* is a continuation 

 of the lamellated sheath of the nerve-branch, and is furnished with a 

 double layer of polygonal nucleated endothelial cells, like those in the 

 lamellated sheath itself. At the central part of the Pacinian body the 

 capsules are absent, leaving a narrow elon- 

 gated space, known as the "interior bulb," 

 surrounded by an endothelial layer continuous 

 with that of the sheath of Henle. Into this 

 interior bulb the ultimate nerve fibre pene- 

 trates, often after repeated division of its parent 

 fibre, and at the same time becomes divested 

 of its medullary layer. The cylinder axis then 

 runs longitudinally through the central part 

 of the interior bulb toward its peripheral ex- 

 tremity, where it exhibits a fibrillated appear- 

 L EXTREMITY OF THE ance, and ends in one or more fungus-like tufts, 



INTERIOR BULB OF A PACINIAN or "terminal buds," which appear like radiated 



BODY; showing the fibrillated . 



texture of the axis cylinder and expansions 01 its Component Ilbrillae. 



its terminal buds. (Key and The end-bulbs in the conjunctiva are similar 

 in form to the Pacinian bodies, but of much 



smaller size, measuring in man from one-third to one-half a millimetre 

 in length. They have only a single capsule, continuous with the sheath 

 of Henle accompanying the nerve fibre. The nerve fibre, as in the fore- 

 going description, loses its medullary layer after reaching the base of 

 the bulb, and enters its interior as a pale, slender axis cylinder. In the 

 calf, the axis cylinder sometimes runs nearly straight through the bulb 

 toward its farther extremity, where it terminates in a fungus-like tuft, 

 like those of a Pacinian body. In man, it makes a number of turns 

 within the bulb, where it finally disappears, apparently by dispersion 

 of its fibrilla3. 



The termination of nerve fibres in muscular tissue has been studied 

 in many animals, both in the fresh condition and with the aid of stain- 

 ing and hardening preparations. No one of these methods has been 

 found to demonstrate fully the anatomical features of the nervous ter- 

 mination ; but by combining the results obtained from all, histologists 

 have acquired a certain degree of knowledge in this respect, which may 

 be summed up as follows. In general, a striped muscular fibre is sup- 

 plied with only a single ultimate nerve fibre ; but this nerve fibre, on 



* Anatornie des Nervensysteins und des Bindegewebes, Stockholm, 1876. Zweite 

 Hiilfte, p. 176. 



