CHARACTERS OF AYES. 489 



posed of two, or sometimes three, phalanges (fig. 213, p\ At 

 the proximal end of this metacarpal, at its outer side, there is 

 generally attached a single phalanx, constituting the so-called 

 "thumb" (fig. 213, /), which carries the "bastard- wing." The 

 digit which is attached to the ulnar metacarpal corresponds to 

 the " ring-finger," and never consists of more than a single 

 phalanx (fig. 213). 



As regards the structure of the posterior extremity or hind- 

 limb, the pieces which compose the innominate bones (namely, 

 the ilium, ischium, and pubes) are always anchylosed with one 

 another; and the two innominate bones are also always an- 

 chylosed, by the medium of the greatly-elongated ilia, with the 

 sacral region of the spine. In no living bird, however, with 

 the single exception of the Ostrich, are the innominate bones 

 united in the middle line in front by a symphysis pubis. The 

 stability of the pelvic arch, necessary in animals which sup- 

 port the weight of the body on the hind-limbs alone, is amply 

 secured in all ordinary cases by the anchylosis of the ilia with 

 the sacrum. 



As in the higher Vertebrates, the lower limb (fig. 214, A) 

 consists of a femur, a tibia and fibula, a tarsus, metatarsus, and 

 phalanges ; but some of these parts are considerably obscured 

 by anchylosis. The femur or thigh-bone (fig. 214, A,/) is 

 generally very short, comparatively speaking. The chief bone 

 of the leg is the tibia (/), to which a thin and tapering fibula (r) 

 is anchylosed. The upper end of the fibula, however, articu- 

 lates with the external condyle of the femur. The ankle-joint 

 is placed, as in Reptiles, between the proximal and distal 

 portions of the tarsus. The proximal portion of the tarsus is 

 undistinguishably amalgamated with the lower end of the tibia. 

 The distal portion of the tarsus is anchylosed with the whole 

 of the metatarsus to constitute the most characteristic bone in 

 the leg of the Bird the " tarso-metatarsus " (m). In most of 

 the long-legged birds, such as the waders, the disproportionate 

 length of the leg is given by an extraordinary elongation of the 

 tarso-metatarsus. 



The tarso-metatarsus is followed inferiorly by the digits of 

 the foot. In most birds the foot consists of three toes directed 

 forwards and one backwards four toes in all. In no wild 

 bird are there more than four toes, but often there are only 

 three, and in the Ostrich the number js reduced to two. In 

 all birds which have three anterior and one posterior toe, it is 

 the posterior thumb or hallux (that is to say, the innermost 

 digit of the hind-limb) which is directed backwards ; and it 

 invariably consists of two phalanges only. The most internal 



