AVES. 555 



may have a naked or waxy appearance, whicli is known as the cere. Below the 

 tarsal joint the extremity is usually covered with horny scales or plates, but 

 some breeds of domesticated birds are " feathered to the ground." The pedal 

 digits of the natatores in each limb are joined by a membrane, which is 

 covered with scaly skin, forming the web-foot. In the domestic fowl the claws 

 are blunt and very strong, that bird being a good example of the order 

 Kasores, or scratchers. The glands of the skin are few, but in many birds, and 

 notably in aquatic species, there is a large gland in the skin of the uropygiiim, 

 or basis of the tail ; this gland secretes an oily sebaceous fluid, which is 

 employed by the animal in dressing or preening its feathers. The combs or 

 wattles, which are the red or sometimes blue processes formed about the heads 

 of certain birds, are very vascular and often erectile structures, appendages of 

 the integument. 



