THE HAIRS. 1389 



The numerous nerves within the highly sensitive integument are chiefly the 

 peripheral processess of sensory neurones which terminate in free arborizations between 

 the ephithelial elements of the cuticle, or in relation with special endings located, for 

 the most part, within the corium or subdermal connective tissue. Some sympathetic 

 fibres, however, are present to supply the tracts of involuntary muscle that occur within 

 the walls of the blood-vessels or in association with the hairs and the sweat glands. 



On entering the skin the medullated nerves traverse the subdermal layer, to 

 which they give off twigs in their ascent, and, passing into the corium, within the 

 papillary stratum divide into a number of branches. Those destined for the epidermis 

 beneath the latter break up into many fibres which, losing their medullary substance, 

 enter the cuticle and end in arborizations that ramify between the epithelial cells as far 

 as the outer limits of the stratum germinativum. The ultimate endings of the fibrillae, 

 whether tapering or slightly knobbed, always occupy the intercellular channels and are 

 never directly connected with the substance of the epithelial elements. According to 

 Merkel, special tactile cells, (Fig. 867) occur in the human epidermis, particularly 

 over the abdomen and the thighs. These cells, spherical or pyriform in shape and 

 composed of clear cytoplasm, occupy the deeper layers of the cuticle and, on the side 

 directed towards the corium, are in contact with the end-plate or meniscus of the nerve. 



The nerve-fibres particularly concerned with the sense of touch terminate within 

 the connective tissue portion of the skin, either within the corium in special end-organs 

 the tactile bodies of Meissner, the end-bulbs of Krause, the genital corpuscles and 

 the end-organs of Ruffini, or within the subdermal layer in the Vater-Pacinian cor- 

 puscles, or their modifications, the Golgi-Mazzoni corpuscles. The structure of these 

 special end-organs is elsewhere described (pages 1018, 1019), their chief locations 

 being here noted. 



Meissner's corpuscles (Fig. 872) are especially numerous in the tactile 

 cushions on the flexor surface of the hands and feet. While much more plentiful in 

 all the tactile pads than in the intervening areas, the touch corpuscles are most 

 abundant in those on the volar surface of the distal phalanges, where they approxi- 

 mate twenty to the square millimeter (Meissner). Their favorite situation is the 

 apex of the papillae, where they appear as elongated elliptical bodies, sometimes in 

 pairs, whose outer pole lies immediately below the epidermis. These corpuscles are 

 additionally, although sparingly, distributed on the dorsum of the hand, the flexor 

 surface of the forearm, the lips, the eyelids, the nipple and the external genital organs. 



The Vater-Pacinian corpuscles (Fig. 874) are well represented in the hands 

 and feet and usually occupy the subdermal tissue, although sometimes found within the 

 corium. Their distribution corresponds closely to that of Meissner's corpuscles, they 

 being most numerous beneath the tactile cushions in the order above described. 



The Golgi-Mazzoni corpuscles are modifications of the Pacinian bodies and, 

 like the latter, are found within the subdermal tissue. 



The end-bulbs of Krause (Fig. 869) occur within the corium, either slightly 

 below or within the papillae, on the lips and external genital organs, as well as 

 probably in other regions. 



The genital corpuscles (Fig. 870) lie within the corium of the modified skin 

 covering the glans penis and the prepuce and the clitoris and surrounding parts of 

 the nymphae. 



The end-organs of Ruffini resemble the sensory terminations in tendons 

 (page 1017) and lie within the deeper parts of the corium, often associated with the 

 Pacinian bodies. 



The mode of ending of the nerves supplying the hairs and sweat glands will be 

 described in connection with those structures (pages 1394, 1400). 



THE HAIRS. 



The appendages of the skin the hairs, nails and cutaneous glands are all 

 specializations of the epidermis and are. therefore, exclusively of ectoblastic origin. 



The hairs (pili) are present over almost the entire body, the few localities in 

 which they are absent being the flexor surface of the hands and feet, the extensor 

 aspect of the terminal segment of the fingers and toes, the inner surface of the 



