THE SKIN AND ITS APPENDAGES. 1139 



sists of numerous small, highly sensitive, or vascular eminences, the papilla?, which 

 rise perpendicularly from its surface. The papillae are conical-shaped eminences, 

 having a round or blunted extremity, occasionally divided into two or more parts and 

 are received into corresponding pits on the under surface of the cuticle. Their 

 average length is about T ^ of an inch, and they measure at their base ^^ of an 

 inch in diameter. On the general surface of the body, more especially in those 

 parts which are endowed with slight sensibility, they are few in number, short, 

 exceedingly minute, and irregularly scattered over the surface ; but in some situa- 

 tions, as upon the palmar surface of the hands and fingers, upon the plantar surface 

 of the feet and toes, and around the nipple, they are long, of large size, closely 

 aggregated together, and arranged in parallel curved lines, forming the elevated 

 ridges seen on the free surface of the epidermis. Each ridge contains two rows of 

 papillae, and between the two rows the ducts of the sweat-glands pass outward to 

 open on the summit of the ridges. In structure the papillae consist of very small 

 and closely interlacing bundles of finely fibrillated tissue, with a few elastic fibres ; 

 within this tissue is a capillary loop, and in some, especially in the palms of the 

 hands and fingers, there are tactile corpuscles. 



The arteries supplying the skin form a network in the subcutaneous tissue, from 

 which branches are given off to supply the sweat-glands, the hair-follicles, and the 

 fat. Other branches are given off which form a plexus immediately beneath the 

 corium ; from this fine capillary vessels pass into the papillae, forming, in the smaller 

 papillae, a single capillary loop, but in the larger a more or less convoluted vessel. 

 There are numerous lymphatics supplied to the skin which form two networks, super- 

 ficial and deep, communicating with each other and with those of the subcutaneous 

 tissue by oblique branches. They originate in the cell-spaces of the tissue. 



The nerves of the skin terminate partly in the epidermis and partly in the cutis 

 vera. The former are prolonged into the epidermis from a dense plexus in the 



Stratum 



XniL ^T-^-j-jf^-C - ISpis granulosum. 



Ft rat >i HI ciinn'/ii 

 of /In 1 mill 



groove. 



Blood-refsel. 



FIG. 680. Longitudinal section through human nail and its nail groove (sulcus). (From Bohm and 



DavulofF s HMolo'ju). 



superficial layer of the corium and terminate between the cells in bulbous extremi- 

 ties ; or, according to some observers, in the deep epithelial cells themselves. The 

 latter terminate in end-bulbs, touch-corpuscles, or Pacinian bodies, in the manner 

 already described ; and, in addition to these, a considerable number of fibrils are 

 distributed to the hair-follicles, which are said to entwine the follicle in a- circular 

 mariner. Other nerve-fibres are supplied to the plain muscular fibres of the hair- 

 follicles (arrectores pili) and to the muscular coat of the blood-vessels. These are 

 probably non-medullated fibres. 



The appendages of the skin are the nails, the hairs, the sudoriferous and seba- 

 ceous glands, and their ducts. 



The nails and hairs are peculiar modifications of the epidermis, consisting 

 essentially of the same cellular structure as that tissue. 



The nails (Figs. 680, 681) are flattened, elastic structures of a horny texture, 

 placed upon the dorsal surface of the terminal phalanges of the fingers and toes. 

 Each nail is convex on its outer surface, concave within, and is implanted by a 

 portion, called the root, into a groove in the skin ; the exposed portion is called the 



