GLANDS OF THE SKIN 393 



and tear to which it is subjected. The columnar cells of the deepest layer 

 of the rete mucosum elongate, multiply by division, the new cells produced 

 being pushed toward the free surface of the skin. There is thus a constant 

 production of fresh cells in the deeper layers, and a constant throwing off of 

 old ones from the free surface. When these two processes are accurately 

 balanced, the epidermis maintains its thickness. When by intermittent 

 pressure a more active cell-growth is stimulated, the production of cells ex- 

 ceeds their waste and the epidermis increases in thickness, as we see in the 

 horny hands of the laborer. 



The dermis, or cutis vera or true skin, is a dense and tough, but yielding 

 and highly elastic structure supporting the epidermis. It is composed of 

 areolar connective tissue interwoven in all directions and forming numerous 

 spaces by its interlacements. These areolae in the deeper layers of the cutis 

 are usually filled with little masses of fat, figure 305. Unstriped muscu- 



FIG. 306. Terminal Tubules of Sudoriferous Glands, Cut in Various Directions. From the 

 skin of the pig's ear. (V. D. Harris.) 



lar fibers are also abundantly present, especially in the skin of animals which 

 erect the hairs with greater ease than is usually the case with man. 



There is a rich network of blood-vessels to the dermis. In the dermal 

 papillcc and about the sweat glands there are special loops of capillaries. 

 Nerve fibers are also distributed to the papillae. 



The special nerve terminations in the skin have been described on page 72. 



Glands of the Skin. The skin possesses glands of two kinds: 

 Sudoriferous or Sweat Glands, and the Sebaceous or Oil Glands. 



A Sudoriferous or Sweat Gland consists of a small lobular mass, formed 

 of a coil of tubular gland-duct, surrounded by blood-vessels, and embedded 

 in the subcutaneous adipose tissue, figure 305, C. The duct ascends from 

 this coiled mass for a short distance in a spiral manner through the cutis 

 and the epidermis, and then opens on the surface of the skin. In the 

 parts where the epidermis is thin, the ducts themselves are thinner and 

 more nearly straight in their course, 



