SENSORY AND TACTILE SENSATIONS. 



FIG. 336. Grandry-Merkel Corpuscles: 

 A consisting of 3 cells; B of 2 cells; 

 n, nerve (tongue of the duck). 



spherical connective-tissue sheath of numerous closely grouped cells, between 

 which the terminal fibrils of the nerves end (Fig. 334). Waldeyer compares these 

 cells with those of the Grandry-Merkel corpuscles. These structures evidently 

 are closely allied to the genital and articular corpuscles. The first appear to be 

 end-bulbs fused together in varying degree in the skin of the glans penis and 



clitoridis. The joint-corpuscles are found 

 in the synovial membrane of the finger- 

 joints; they are larger than the end-bulbs, 

 and exhibit on the outer surface numerous 

 oval nuclei ; as many as four nerves pene- 

 trate their interior. 



The Grandry-Merkel corpuscles occur 

 in the so-called waxy covering of the 

 bill, and in the tongue of ducks and 

 geese. They are large cells with spherical 

 nuclei and nucleoli, surrounded by a 

 fibrous sheath, and between them a naked 

 nerve-fiber is interposed by means of a 

 protoplasmic disc tactile disc. Two or 

 more cells are often found on top of one 

 another, with a nerve-end disc between 



them. When a number of such cells are placed upon one another and side by 

 side larger structures are produced that appear to be transitional forms to the 

 tactile corpuscles. In animals there are many other kinds of terminal corpuscles 

 on the sensory nerves: The corpuscles of Hefbst in birds, resembling small cor- 

 puscles of Vater, with longitudinal striation in the periphery and transverse 

 striation within, but without a distinct capsule; the tactile cones in the snout 

 of the mole and allied animals; the end-capsules on the penis of the hedgehog, 

 and on the tongue of the elephant; the tactile bulbs on the beak and the tongue 

 of several birds ; the nerve-rings 

 in the auricles of the mouse. 

 Terminal ganglion-cells, con- 

 nected with cilia, form the 

 tactile organ in the rotifera, 

 crustaceans, and insects. 



The termination of the 

 nerves by means of most deli- 

 cate fibrils with knob-like 

 ends (terminal nodules) be- 

 tween the epithelial cells of 

 the cornea has already been 

 described (p. 816). A similar 

 arrangement exists also be- 

 tween the cells of the epider- 

 mis and between the epithelial m 

 cells of the genital organs. 



In sensitive situations the 

 peripheral ends of the nerve- 

 fibers form distinct patelliform 

 tactile discs (tactile menisci) 

 within the epidermis, and upon 



them the lower cells of the Malpighian layer are placed. These structures are 

 found in man and in animals, for example in the snout of the pig (Fig. 337). 



On the hairs, which are in many places connected with the tactile apparatus, 

 there is below the opening of the sebaceous gland a nervous end-organ in the 

 external root-sheath, consisting of longitudinal and circular fibers, forming a 

 network. Tactile discs are present in the cells of the outer root-sheaths of the 

 tactile cilia in mammals. 



FIG. 337. Tactile Discs with Nerves from the Epidermis 

 (snout of the pig): c, epidermal cells; a, tactile cells; 

 m, tactile discs; , nerve. 



SENSORY AND TACTILE SENSATIONS. 



The sensory nerve-trunks contain two functionally different sets of 

 nerve-fibers, namely: (i) Those that convey painful sensations, and 

 are sensory nerves in the narrow sense of the word, and (2) those 



