STRUCTURE OF APPENDAGES 



The skin of the fowl is very thin and does not contain oil glands or 

 sweat glands. In the fowl the oil is supplied by a tail or rump gland, 

 the glandula uropygii (Fig. 35, No. 16). This gland is round or oval 

 in shape, and about the size of a pea and consists of two lobes. It 

 is of the tubular variety with a teat, which, in most instances has two 

 openings. A medium septum divides the gland into two halves. 

 The oil secreted by the columnar epithelial cells is collected in a 

 body cavity located in the center of the gland; this has a duct extend- 

 ing to the surface. The bird by squeezing out a quantity of this 

 oil into its beak oils the feathers, passing the beak over them, one 

 by one. The oil renders the feathers practically impervious to 

 water. It is necessary for the bird to give proper attention to its 

 plumage in order that the feathers appear in prime condition. Should 

 there be a disease of the oil gland, or should the bird become ill and 

 neglect its toilet the result is an unkempt appearance of the plumage, 

 the feathers becoming rather rough and more or less injured by the 

 weather. 



The subcutis is well developed and furnishes to the cutis great 

 capability for movement, which is necessary for the rising and fall- 

 ing of the feathers. The corneum is very thin. Papillary bodies 

 are present only in a very few places, such as the region about the 

 eye and on the toes. Where the toes touch the ground in walking 

 there are large wart-like thickenings of the epithelium. In most 

 birds the shanks are unfeathered. The epidermis on the feathered 

 parts of the skin is thin, dry on the surface, and abounds in continu- 

 ous scales. The stratum corneum is very thick on the horny sheath 

 of the beak, on the top of the toes, on the spurs of the cock, and 

 on the scale plates that cover the skin on the shanks. The feathers 

 of birds serve the same protective purpose as hair on mammals. 

 In cold weather the skin muscles controlling the feather movements 

 contract; thus the feathers become ruffled much as we observe the 

 hair standing erect on horses under similar conditions. By increas- 

 ing the dead air space around the body, the radiation of heat is re- 

 tarded, and the body kept warmer. The corneum of the skin is not 



309 



