BIRDS. 175 



fourteen, and in the Gallinae eighteen. The legs have a femur 

 and a tibia, and the tarsus and metatarsus are represented by a 

 single bone. The toes are attached to the tarsus, and are ge- 

 nerally three before and a kind of thumb behind, which, how- 

 ever, is sometimes wanting. In the swallow it is directed for- 

 wards. In the climbers, on the contrary, the external toe and 

 the thumb are directed backwards. The number of joints in- 

 creases in each toe, counting from the thumb, which has two, to 

 the external toe, which has five. Birds with the toes entirely 

 free are adapted to walk or hop on a horizontal surface, such 

 as the domestic fowl. Others with two toes behind and two 

 before, such as the parrot, walk with difficulty, but climb with 

 facility ; and others again, such as ducks and swans, with the 

 toes united by a membrane, are chiefly calculated for motion in 

 water. 



The bill in birds is covered with a corneous substance, and as 

 these animals swallow their food without mastication, they are 

 not furnished with teeth. The upper mandible is formed chief- 

 ly of the intermaxillary bones, prolonged behind into two arch- 

 es, of which the internal is composed of the palate bones, and 

 the external of the maxillary and jugal bones ; and this mandi- 

 ble is united to the cranium by elastic laminae. The bill is 

 constructed less for bruising the food than for seizing and di- 

 viding it ; and thus from the greater solidity and length of this 

 organ the nature of the food may be inferred. 



The bill or bea'k is sometimes furnished at its origin with a 

 fleshy or membranous caruncle, which is called the cere ; and 

 sometimes the beak is prolonged upon the forehead into a kind 

 of horn or helmet, as in the Calao. The two mandibles, move- 

 able upon one another through the medium of an intermediate 

 bone placed at the articulation, is a distinguishing anatomical 

 character in the structure of the jaws of birds. 



The quills and feathers are composed of a bearded or webbed 

 stem hollowed at its base ; these webs or horizontal feathers are 

 again themselves webbed by still smaller ones ; and the tex- 

 ture, the strength, lustre, and general form of these feathers 

 are infinitely varied. The feathers fall off* twice a-year, and 

 this change of plumage is termed moulting. In some species 

 the winter plumage differs from that of summer, and in the 



