OH. LI.] 



TACTILE END-ORGANS. 



695 



Pacini. They are little oval bodies, situated on some of the cerebro- 

 spinal and sympathetic nerves, especially the cutaneous nerves 

 of the hands and feet, where they lie deeply placed in the true 

 skin. They also occur on the nerves 

 of the meseutery of some animals like 

 the cat. They have been observed 

 also in the pancreas, lymphatic glands 

 and thyroid glands, as well as in the 

 penis. They are about ^V inch long. 

 Each corpuscle is attached by a narrow 

 pedicle to the nerve on which it is 

 situated, and is formed of several 

 concentric layers of membrane, con- 

 sisting of a hyaline ground-membrane 

 with connective-tissue fibres, each layer 

 being lined by endothelium (figs. 514, 

 515); through its pedicle passes a single 

 nerve-fibre, which, after traversing the 

 several concentric layers and their in- 

 termediate spaces, loses its medullary 

 sheath and enters a central core, at or 

 near the distal end of which it termi- 

 nates in an arborisation. Some of these 

 layers are continuous with those of 

 the perineurium, but some are super- 

 added. In some cases two nerve-fibres 

 have been seen entering one Pacinian 

 body, and in others a nerve-fibre after passing unaltered through 

 one has been observed to terminate in a second Pacinian corpuscle. 



The corpuscles of Herbst (fig. 516) are closely allied to 

 Pacinian corpuscles, except that they are smaller and longer with 

 a row of nuclei around the central termination of the nerve in the 

 core. They have been found chiefly in the tongues and bills of 

 ducks. The capsules are nearer together, and towards the centre 

 the endothelial sheath appears to be absent. 



End-bulbs are found in the conjunctiva (where in man they 

 are spheroidal, but in most animals oblong), in the glans penis 

 and clitoris, in the skin, in the lips, in the epineurium of nerve- 

 trunks, and in tendon ; each is about ^^ mcn m diameter, oval 

 or spheroidal, and is composed of a medulluted nerve-fibre, which 

 terminates among cells of various shapes. Its capsule contains 

 a transparent or striated core, in the centre of which terminates 

 the axis-cylinder of the nerve-fibre, the ending of which is 

 somewhat clubbed (fig. 517). 



- 5'3- Extremities of a nerve 

 of the finger with Pacinian 

 corpuscles attached, about 

 the natural size. (Adapted 

 from 1 1 en If and Kolliker.) 



