ANATOMY OF THE FOWL 41 



The muscles of the skin are well developed in certain parts 

 of the body. They are divided into primary and secondary 

 muscles. The secondary muscles are branches of the skeletal 

 muscles. On the feathered parts of the skin the epidermis is 

 thin, rather dry on the surface and is provided with continu- 

 ous scale-like layers. The stratum corneum is thick on the 

 horny sheath of the beak, on the dorsal surfaces of the toes, the 

 spurs of the cock, and the scaly plates of the shanks. The 

 feathers covering the surface of the body represent a special 

 epidermal formation, analogous to the hair of animals. Feath- 

 ers occur over the whole surface of the body except on cer- 

 tain parts of the under surface, and the neck, shanks and 

 toes. Some breeds are provided with a row on the outer edge 

 of the shanks and outer toe. The corium is not very rich in 

 blood vessels. It forms a thick net-like structure in the comb, 

 gills and similar appendages of chickens and turkeys. The 

 only gland that is present is the tail (rump) gland (glandula 

 uropygii). The gland is round or oval and in fowls the size 

 of a pea. In geese it is the size of a hazelnut. A median 

 septum divides the gland into two halves ; at times there may 

 be found two ducts leading from this gland, but there is 

 usually only one. The gland is largest in swimming birds. 

 The gland is a tubular one and is provided with a sinus into 

 which the cells pour their secretion. The corium often con- 

 tains mucous sacs. 



The feathers develop from a papillary structure of the 

 corium. This corresponds to the hair papilla of mammals. 

 The feather is divided into a quill, a midrib or shaft, primary 

 and secondary barbs. The free end of the quill occupies the 

 papilla of the skin and is roundish, rather three-sided in 

 shape. It is hollow, with thin dividing septa. It has a cup- 

 shaped depression at the free end which surrounds the feather 

 papilla and includes a horny mass. The shaft is provided with 

 four sides and four edges and is solid. It contains a white 

 spong}^ substance. From the sides of the shaft the primary 

 barbs extend out, and in most breeds on either border of these 

 primary barbs Ave find secondary barbs or barbules which 

 dovetail into the secondary barbs or barbules of the adjacent 

 barb. Tliese form the web of the feather. There are no bar- 

 bules in the fluffy portion of the feather nor in feathers of the 

 silky breeds. 



The feather coat is changed twice a year, either in late 

 summer or fall, and in spring or early summer. A chick 

 molts four times before growing its adult feathers. 



