596 AVES BIRDS. 



mere rudiment when present, is an appendage to tlie radial side of 

 the carpus. 



In the pelvic extremity (Jig. 268) the femur is a short and strong 

 bone : to this succeeds the tibia, upon the outer side of which is 

 fixed a rudiinental^fttf/a. The tarsus can scarcely be said to exist, 

 being at a very early age confused with the metatarsus ; the whole 

 forming a single tarso-metatarsal bone, which, in the Wading Birds 

 especially, is of very great length : at its distal extremity are 

 three articular surfaces that support the three anterior toes, while 

 a fourth toe, the hallux, directed backwards, is attached to it 

 posteriorly by the intervention of a small accessory piece ; and in 

 Gallinaceous Birds an osseous spur, consolidated with the posterior 

 face of the tarso-metatarsal bone, is generally considered as a fifth 

 toe. 



The number of toes varies in different tribes of birds. Thus, in 

 the Ostrich there are only two ; in many genera there are three ; in 

 by far the greater number, four ; and in the Gallinacea, five. But 

 whatever the number of toes may be, the number of phalanges pe- 

 culiar to each is remarkably constant : thus, the outermost toe 

 always consists of five phalanges; the fourth toe invariably of four; 

 the third as constantly of three ; the second, when it exists, has 

 only two ; and, lastly, in the spur or innermost toe there is but a 

 single piece. 



(662.) So rapidly is the progress of ossification accomplished in 

 the skeleton of a bird, that it is only in very young animals the indi- 



Fig. 270. 



vidual bones or elements composing the cranium can be identified, 

 as the sutures speedily become obliterated : when, however, they 



