THE INTEGUMENT AND THE EXOSKELETON in 



the inner aspect of the femora; at the time of pairing these 

 secrete a gummy fluid which hardens into short spines or teeth, 

 employed during copulation. In birds the sole integumental 



Stratum corneum i 



Stratum lucidum [ Epidermis 



Stratum mucosum j 



" Corium 



FIG. 30. Typical mammalian hair with its accessory parts. [After 

 WEBER.] 



67. ac., acinous gland, usually sebaceous; Gl. tb., tubular gland, usually per- 

 spiratory in function; M, ar. pil., arrector pilarum muscle. 



gland is the uropygial, a compound mass situated on the dorsal 

 aspect of the tail rudiment, and secreting an oily fluid used 

 for anointing the feathers. 



In mammals, the skin is, as a rule, profusely glandular, and 

 the glands possess the highest degree of physiological dif- 

 ferentiation. In spite of their diversity, however, they may 



