92 GENERAL ANATOMY. 



double row, with smaller papillae between them ; and these rows are subdivided 

 into small square-shaped spaces by short transverse furrows, regularly disposed ; 

 in the centre of each of these transverse furrows is the minute orifice of the duct 

 of a sweat-gland. No papillae exist in the grooves between the ridges. In 

 structure the papillae consist of very small and closely interlacing bundles of 

 finely fibrillated tissue, with a few elastic fibres. The majority of the papillae con- 

 tain loops of blood-vessels, and these are known as the vascular papillae in contra- 

 distinction to others which usually possess no blood-vessels, but contain tactile cor- 

 puscles. These tactile papillae are most numerous in the derma of the palm of the 

 hand and of the sole of the foot, but occur also in smaller numbers on the back 

 of the hand and foot, on the flexor surface of the forearm, and on the nipple. 



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, superficial 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 form a dense plexus in the superficial layer of the corium, 

 which extends horizontally and gives off numerous fibrils ; these are prolonged 

 into the epidermis, and terminate between the cells, either in bulbous extremities 

 or in a network ; or, according to some observers, in the deep epithelial cells them- 

 selves. 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 manner. Other nerve-fibres are supplied to the plain 

 muscular tissues of the hair-muscles (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 

 sebaceous 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 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 body, and the 

 anterior extremity the free edge. The nail has a very firm adhesion to the cutis, 

 being accurately moulded upon its surface, as the epidermis is in other parts. The 

 part of the cutis beneath the body and root of the nail is called the matrix, because 

 it is the part from which the nail is produced. Corresponding to the body of the 

 nail, the matrix is thick, and covered with large, highly vascular papillae, arranged 

 in longitudinal rows, the color of which is seen through the transparent tissue. 

 Behind this, near the root of the nail, the papillae are small, less vascular, and 

 have no regular arrangement, and here the tissue of the nail is somewhat more 

 opaque ; hence this portion is of a whiter color, and is called the lunula on 

 account of its shape. 



The cuticle, as it passes forward on the dorsal surface of the finger or toe, is 

 attached to the surface of the nail, a little in advance of its root ; at the extremity 

 of the finger it is connected with the under surface of the nail a little behind its 

 free edge. The cuticle and horny substance of the nail (both epidermic structures) 

 are thus directly continuous with each other. The nails, in structure, consist of 

 cells having a laminated arrangement, and these are essentially similar to those 

 composing the epidermis. The deepest layer of cells, which lie in contact with 

 the papillae of the matrix, are of elongated form, arranged perpendicularly to the 



