TERMINATIONS OF SENSORY NERVES. 



829 



connective-tissue capsule continuous with Henle's sheath of the nerve, and enclosing many cells, 

 amongst which the axis-cylinder which enters the bulb branches and terminates.] The spheroidal 

 end-bulbs occur in man, in the nasal mucous membrane, conjunctiva, mouth, epiglottis, and 

 the mucous folds of the rectum. According to Waldeyer and Longworth, the nerve-fibrils 

 terminate in the cells within the capsule. These cells are said to be comparable to Merkel's 

 tactile cells ( Waldeyer). 



The genital corpuscles of Krause, which occur in the skin and mucous membrane of the 

 glans penis, clitoris, and vagina, appear to be end-bulbs more or less fused together (fig. 612). 



The articulation nerve -corpuscles occur in the synovial mucous membrane of the joints of 

 the fingers. They are larger than the end-bulbs, and have numerous oval nuclei externally, 

 while one to four nerve-fibres enter them. 



4. Tactile or touch-corpuscles of Merkel, sometimes also called the corpuscles of Grandry, 

 occur in the beak and tongue of the duck and goose, in the epidermis of man and mammals, 

 and in the outer root-sheath of tactile hairs or feelers (fig. 613). They are small bodies com- 

 posed of a capsule enclosing two, three, or more large, granular, somewhat flattened nucleated 

 and nucleolated cells, piled one on the other in a vertical row like a row of cheeses. Each 

 corpuscle receives at one side a medullated nerve-fibre which loses its myelin, and branches, to 

 terminate, according to some observers {Merkel), in the cells themselves, and according to others 

 (Ranvier, Izquierdo, Hesse) in the protoplasmic transparent substance or disc lying between 

 the cells. [This intercellular disc is the "disc tactil" of Ranvier, or the " Tastylatte" of 

 Hesse.] When there is a great aggre- 

 gation of these cells, large structures are 

 formed which appear to form a kind of 

 transition between these and touch- 

 corpuscles. [According to Klein, the 

 terminal fibrils end neither in the touch- 

 cells nor tactile disc, but in minute 



mmmm 



it^SMl 



SlffipK^r^- 



'71 



Fig. 614. 

 613. Tactile corpuscles from the duck's tongue. A, composed of three cells with two 

 interposed discs, with axis-cylinder, n, passing into them. B, two tactile cells and one 

 disc. Fig. 614. Bouchon epidermique from the groin of a guinea-pig, after the action of 

 gold chloride, n, nerve-fibre ; a, tactile cells ; ra, tactile discs ; c, epithelial ceils. 



swellings in the interstitial substance between the touch-cells, in a manner very similar to that 

 occurring in the end-bulbs. ] 



[According to Merkel, tactile cells, either isolated or in groups, but in the latter case never 

 forming an independent end-organ, occur in the deeper layers of the epidermis of man and 

 mammals and also in the papillae. They consist of round or flask-shaped cells, with the lower 

 pointed neck of the flask continuous with the axis-cylinder of a nerve-fibre. They are regarded 

 by Merkel as the simplest form of a tactile end-organ, but their existence is doubted by some 

 observers. ] 



Amongst animals there are many other forms of sensory end-organs. [Herbst's corpuscles 

 occur in the mucous membrane of the tongue of the duck, and resemble small Vater's corpuscles, 

 but their lamellae are thinner and nearer each other, while the axis-cylinder within the central 

 core is bordered on each side by a row of nuclei.] In the nose of the mole there is a peculiar 

 end-organ {Eimer), while there are " end-capsules'" in the penis of the hedgehog and the tongue 

 of the elephant, and " nerve-rings " in the ears of the mouse. 



5. [Other Modes of Ending of Sensory Nerves. Some sensory nerves terminate not by means 

 of special end-organs, but their axis-cylinder splits up into fibrils to form a nervous network, 

 from which fine fibrils are given off to terminate in the tissue in which the nerve ends. These 

 fibrils, as in the cornea ( 384), terminate by means of free ends between the epithelium on the 

 anterior surface of the cornea, and some observers state that the free ends are provided with 

 small enlargements ("boutons terminals") (fig. 614, a). These enlargements or "tactile cells" 

 occur in the groin of the guinea-pig and mole. A similar mode of termination occurs between 

 the cells of the epidermis in man and mammals (fig. 293).] 



6. Tendons, especially at their junction with muscles, have special end-organs (Sachs, Rollett, 

 Golgi), which assume various forms ; it may be a network of primitive nerve-fibrils, or flattened 



