AVES. 283 



Ostrich, they do not unite below, but remain separate. As in the 

 higher Vertebrates, the lower limb consists of a thigh-bone {femur), 

 a shank, composed of two bones (fihia and fibula), a tarsus, a meta- 

 tarsus, and phalanges, but some of these parts are obscured by 

 coalescence. The thigh-bone or femur (fig, 204, /), is generally 

 very short, comparatively speaking ; and the chief bone of the leg 

 is the tibia (t), to which a thin and tapering fibula (r) is attached. 



Fig. 204. — A, Pelvis and bones of tlie leg of the Loon or Diver (after Owen) ; i Innomi- 

 nate bone ; /ThigU-bone (femur); (Tibia; r Fibula, togetlier forming the shank; 

 m Tarso - metatarsus ; p Phalanges of the toes. B, Tail of the Golden Eagle : s 

 Ploughshare-shaped bone, carrying the great tail-feathers. 



In the regular typical limb of a Vertebrate animal the tibia and 

 fibula would be followed by a series of small bones, called the 

 tarsus, constituting the ankle-joint (fig. 161) ; and the tarsus would 

 in turn be followed by a series of bones constituting the root of the 

 foot, or metatarsus. In Birds, however, the tibia and fibula are 

 followed by a single cylindrical bone, which is called the " tarso- 

 metatarsus " (m), and which is formed by the amalgamation of the 

 three principal metatarsal bones with the lower row of tarsal bones, 



