312 



HITCHCOCK'S ANATOMY 



Fig. 300. Fig. 301. 



A. B. Hairs of Squirrel. C. Hair of Indian Bat. 



latter secrete an unctious fluid, which is usually of a strong 

 smell. 



553. Skin of Birds. — The Skin of Birds is thin and desti- 

 tute of cutaneous glands, except one at the tail, which is gen- 

 erally present. The whole body is covered by feathers, except 

 certain parts of the head, legs, and feet. There it becomes very 

 much thickened, forming callosities, wattles and combs, in 

 which, beside the cellular tissue, are found the elastic and erec- 

 tile tissues, as well as red and blue cells of coloring matter. 

 Upon the toes and feet are found plates and scales of horny tissue. 



554. Feathers of Birds. — The Feathers of Birds are 

 made up of the Quill and Vane: the former giving it attach- 

 ment to the body, and the latter forming its expanded surface. 

 The Vane is made up of a small number of laminae or plates, 

 which both form a light and firmly resisting medium to the 

 air, and serve to retain the heat within the body. When per- 

 fectly formed the laminae are furnished with a hooklet at their 

 free extremities, by which they are attached to each other, 



553. What is the thickness of the shin of birds compared with that of mammals? 

 What are the wattles and combs? 554. What two parts are feathers made up of? Why- 

 are the lamina? furnished with a barb at each extremity? What is the design of their 

 overlapping each other ? 



