VERTEBRATA ^AVE8\ 35 



humerus, which is united to the pectoral arch, and is 

 followed by the radius and ulna. The radius is very 

 slender. Then follow two small carpal bones, and two 

 metacarpal bones, which are anchylosed at both ex- 

 tremities. There is a rudimentary thumb situated at the 

 upper end of the metacarpal bones. This thumb consists 

 of a single joint, and carries the " bastard wing." The 

 metacarpal bones support two " fingers," which corre- 

 spond to the index and middle fingers of the human hand. 

 One of the fingers consists of a single phalanx or joint; 

 the other has two or three. 



Fia. 10. Wma OF A SPARROW. 



With regard to the structure of the hind limb, there 

 is a very short femur united to the " pelvic arch." This 

 is followed by the tibia, to which a very thin fibula is 

 anchylosed. The upper part of the tarsus is amalgamated 

 with the tibia, and the lower portion with the metatarsus, 

 forming the bone called the tarso-metatarsus. In the 

 waders this bone is very long. 



There are usually four toes, but some domestic birds 

 possess a fifth toe. Three of the toes are commonly 

 placed before, and one behind. One group, however, has 

 two before and one behind. The swifts have the whole 

 four directed forwards. In several of the swimmers, and 



