OR OSSEOUS SYSTEM. 



in order to be more under the centre of gravity, to poise 

 alone the entire trunk. The posterior extremities having more 

 of the ordinary use of these members in other animals than 

 the anterior, have their osseous elements constructed more 

 according to the normal character and number of these parts 

 in other vertebrated classes. The head of the femur is small, 

 short, and rounded,, with a very short cervix, and projects 

 at a right angle a little lower than the trochanter major, 

 which here forms an extensive arch from before backwards. 

 The femur (Fig. 45. v,) in birds is generally very short and 

 strong compared with the succeeding bones of the leg, even 

 in the long-legged grallatores, and the running birds. The 

 air is admitted into this hollow bone, by a large aperture on 

 the fore part of the trochanter major. Between the two 

 prominent sharp condyles of the femur and the upper end 

 of the long tibia is placed the patella, as in quadrupeds. At 

 the upper and outer part of this long and strong tibia (Fig. 

 45. w,) is a small, imperfectly formed fibula, thin, tapering, 

 and anchylosed to the tibia at its lower part, and separate 

 above ; sometimes it is separate throughout. The lower 

 part of the tibia presents a broad, expanded, articular sur- 

 face for the succeeding long bone of the meta-tarsus, which 

 is single, like the meta-carpal bone of the hand. There is a 



small tarsal bone in the ostrich, which 

 thus leads to the structure of this part in 

 the lowest ruminantia. The tibia and the 

 meta-tarsal bone are long in most birds, but 

 especially in the wading birds, as cranes and 

 storks. The meta-tarsal bone (Fig. 52. ,) 

 has two articular depressions at its upper 

 part, for the two inferior condyles of the 

 tibia, and at its lower end it commonly pre- 

 sents three pulley-like articular prominences 

 (b,) for the attachment of the three toes, 

 which are directed forwards. It resembles 

 that of the jerboa among the rodentia. 

 There is generally at the inner and back 

 part of this bone another very small meta- 

 tarsal bone (,) for the attachment of the 

 toe which is directed backwards. The 

 outer toe of birds has five phalanges (1 . d,) 



FIG. 52. 



