1158 



THE ORGANS OF SPECIAL SENSE 



The arteries supplying the skin vary in number, and vary much in size, being largest in re- 

 gions exposed to pressure, as the skin of the palms, soles, and buttocks. The arteries enter the 

 .skin from a network in the subcutaneous tissue, and by an anastomosis in the deepest part of the 

 corium form a network (rete arteriosum cutaneum). The vessels send branches to the fat and 

 to the sweat glands. Branches from the network just described ascend and form a second net- 

 work in the corium beneath the papillae. This is called the subpapillary network (rctc artr- 

 riosum subpapillare). From this network 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. 

 From this network branches go to the hair follicles and sebaceous glands. The blood from 

 the papillae passes into a plexus (rete venosum) beneath the papillae. This communicates with 

 another plexus between the corium and subcutaneous tissue. In some regions one or more ret in 

 are interposed between these two. The veins from the sweat glands, sebaceous glands, superficial 

 fat, and hair follicles are received by the retia venosa. From the deepest rete veins pass to 

 the subcutaneous tissue, and these veins enter the large subcutaneous veins. 



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

 and deep, communicating with each other and with the lymphatics 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 (Fig. 867) and partly in the cut is 

 vera (Fig. 866). The former are prolonged into the epidermis from a dense plexus in the super- 

 ficial layer of the corium and terminate between the cells in bulbous extremities; or, according 

 to some observers, in the deep epithelial cells themselves. The latter terminate in end bulbs, 

 touch corpuscles, or Pacinian bodies (Figs. 590 and 866), in the manner already described 

 (p. 819), and, in addition to these, a considerable number of fibrils are distributed to the hair 

 follicles, which are said to entwine about the follicle in a circular manner. Other nerve fibres 

 are supplied to the smooth muscle fibres (mm. arrectort's p//ornni} of the hair follicles and to the 

 muscle coat of the bloodvessels. These are probably amyelinic fibres. 



THE APPENDAGES OF THE SKIN. 



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. 



Eponychium. 



Nail. 



Stratum 



Malpighii, 



Stratum corneum 

 of the nail 

 groove. 



FIG. 871. Longitudinal section through human nail and its nail groove (sulcus). 



Davidoff's Histology.) 



Stratum 

 corneum. 



'Stratum 

 granulosum. 



Corium. 



Blood-vessel. 



(From Bohin and 



The Nails (ungues) (Figs. 871 and 874) are flattened, elastic structures ,,f 

 a horny texture, placed upon the dorsal surface of the terminal phalanges of tin- 

 fingers and toes. Each nail is convex on its outer surface, concave within. Its 

 chief mass, called the body (corpus unguis), lies upon the nail bed. The free edge 

 is called the margo liber. Each lateral margin (margo lateralis), like the proximal 

 short edge of the nail (margo occultus), lies in a groove of the cutis, the ungual sulcus 

 (sulcus matricis unguis). The ungual wall (vallum unguis) overlies the lateral a ml 

 posterior edges. The nail is implanted by means of a portion, called the root 

 (radix unguis), into a groove in the skin. The root is beneath the ungual wall 

 and is composed of cells which have not yet become horny. It is white in color. 

 The nail has a very firm adhesion to the cutis vera, being accurately moulded 



