INTEGUMENT 47 



stratum lucidum represents an advance in degenerative changes 

 in which the keratohyaline granules of the granulosum cells are 

 converted into a substance called eleidin, which gives the stratum 

 lucidum a glassy appearance in sections. The stratum corneum 

 is composed of numerous layers of dead, dry, squamous cells 

 that are constantly rubbed off piecemeal. The loss of cells at 

 the surface of the skin is made good by the production of new 

 cells in the basal layer of the epidermis, whence they spread to 

 the outside. The various layers of the epidermis, above the 

 basal layer, represent progressive stages in cell degeneration. 



The corium of human skin is made up of white and elastic 

 connective tissue fibers, blood vessels, nerves, and glands pro- 

 jecting into it from the epidermal layer. The stratum subcuta- 

 neum lies beneath the corium to which it is firmly attached. It is 

 composed of loose, fibrous connective tissue, with numerous 

 fat cells and is connected below by connective tissue with muscle 

 or with the periosteum of bone. Human skin is more firmly 

 anchored to underlying structures than is the skin of the frog. 



There are no chromatophores in human skin. The color of the 

 skin is due to pigment granules in and among the lowest layers of 

 the epidermis. A few granules are also found in the corium. 



There are two general types of glands in human skin, sweat 

 glands and oil glands. Sweat glands, epidermal in origin, are 

 long unbranched tubes, extending from the surface of the epi- 

 dermis into the deep part of the corium or into the subcutaneous 

 tissue, each tube terminating in a coil. Ordinarily, the secretory 

 cells, located in the coiled portion of the gland, secrete an oily 

 fluid for the lubrication of the skin, but under nervous stimulation 

 the secretion becomes more watery and by evaporation serves to 

 cool the surface of the body. Sebaceous glands, also derived 

 from the epidermis, are branched or unbranched glands located 

 in the upper layer of the corium and usually attached to the 

 sheath of a hair. On the margin of the lip they occur independ- 

 ently of hair. The secretion consists of fat and cell debris. In 

 its production the gland cells fill with fat and then break down, 

 the fat and cell debris forming a semifluid material. The 

 mammary glands, which may be regarded as modified sweat 

 glands, are made up of a branching system of ducts terminating 

 in alveoli, i.e., rounded vesicles, which extend from their point 

 of origin in the epidermis, at the nipple, into the corium and 



