STRUCTURE OF APPENDAGES 313 



quill emerges from the skin there is another small opening, the 

 superior umbilicus, from which springs frequently a small feather 

 called the hyporachis. The shaft, or rachis, has a groove extending 

 along that surface which lies next the body. 



In the newly formed chick the first indication of feathers is the 

 formation of papillae, which is constituted by The upward growth of 

 the dermis, or the sensitive and vascular parts of the skin. Then 

 the skin immediately around the papilla sinks downward, so that 

 later the papilla is inclosed in a follicle of the skin. The epidermis 

 over the papilla is the same as over the rest of the surface. The 

 horny outer layer of the epidermis forms for the growing feather a 

 protective sheath which is cast off as the feather is formed. The 

 feather proper develops from the underlying germinative layer, 

 which as the feather develops, forms a cylinder of cells. The lower 

 part of the cylinder is in touch with the papilla; this later becomes 

 the quill (Fig. 80, No. 2). The upper part of the cylinder develops 

 the web portion of the feather. As soon as the feather is fully 

 developed the papilla, which has projected into the quill and 

 nourished it, is withdrawn, and the quill becomes filled with a pith- 

 like material forming septa, which extend in different directions. 



Once a year, usually in the late summer or in the fall, the entire 

 feather coat is changed. This process is called molting. During 

 this time the bird appears in a somewhat depressed condition, the 

 hen almost always ceases laying. Birds also molt in the spring, 

 to a limited extent. The male at this time takes on the so-called 

 breeding plumage, which is the most beautiful of the year. It has 

 recently been established by Rice, that the young fowl, in reaching 

 a stage of egg production, molts five times before the laying period 

 begins. 



The structure of the skin of fowls is similar to that of the skin of 

 mammals. The skin consists of two layers the outer portion, or 

 epidermis, and the inner true skin, the cutis, corium, or dermis. If 

 we study a section of skin from the shank region of a fowl we find 

 the outer portion is differentiated into two distinct regions, the rete 

 Malpighii and the stratum corneum. The stratum corneum is the 

 outer horny layer. The cells making up this portion are fusiform, 

 flattened, and in regular rows. The nuclei in these layers of cells 

 are not pronouncedly visible, and the outline of the cells not clear 

 in a section such as used in our ordinary methods of study. The 

 corneum is a compact mass of remnant cells which have lost the 



