314 ANATOMY OF THE DOMESTIC FOWL 



appearance and their texture of living cells. It thus becomes 

 modified into scales upon the skin surface. 



Between the stratum corneum and the stratum Malpighii there 

 is another zone which consists of the cells undergoing a transitional 

 stage from a cubical shape to a more flattened appearance, and 

 gradually becoming more granular and hyaline. 



The various parts of the epidermis are in close genetic relation- 

 ship to one another. The upper layer of epithelium is constantly 

 being desquamated. This casting off is compensated for by a 

 continuous upward pushing of its lower elements. Cell prolifera- 

 tion occurs in the basal cells and in adjacent cellular strata of the 

 stratum germinativum, or stratum Malpighii, where the elements 

 are often seen in process of mitosis, or cell division. The young cells 

 are gradually pushed upward. During their course they assume the 

 general characteristics of the elements composing the layers through 

 which they pass. This process is as follows: each cell changes first 

 into a cell of the stratum Malpighii; then, when it commences the 

 formation of keratohyalin, it changes into a cell of the stratum 

 granulosum; later still, into a cell of the stratum lucidum; and finally 

 into an element of the stratum corneum, where it gradually loses 

 its nucleus, cornifies, and at last drops off. 



The mesodermic portion of the skin consists of loose, subcutaneous 

 connective tissue containing some fat. The amount of adipose tissue 

 in the subcutaneous layer is subject to great variation; there are a 

 few places in which there is little or no fat. The upper portion 

 of this layer contains a few elastic fibers, which interlace and run 

 in all directions. Numerous round or oval cells are found in the 

 upper region. The lower and middle portions of the corium are 

 richly supplied with blood-vessels terminating into capillaries, which 

 penetrate the portions bordering the epidermis. Nerves giving off 

 terminal branches also occur. 



The various colors of the skins of fowls are due to the distribution 

 of various quantities of two colors, orange-yellow and brownish-black. 



The yellow pigment is probably carotin and xanthophyll, two 

 pigments contained in association with the chlorophyll of plants, 

 which the bird obtains in its feed. These coloring matters were 

 formerly called lipochrome; but as lipochrome may be any coloring 

 matter of fat, it is not sufficiently definite. This yellow pigment, 

 when present, is diffused through all parts of the cell. When dilute, 

 it gives a yellow hue; when concentrated, orange. It is found in the 



