BIRDS. 75 



lower jaw by means of a quadrate bone, as in the lizards, 

 snakes, etc. 



The shoulder girdle consists of scapula, coracoid, and 

 clavicles, the latter noticeable for their union into a V- 

 shaped " wish-bone " or furcula. In the wing the reduction 

 in bones near the end is remarkable. The bones of the 

 wrist are all united into two, while the tfrree fingers which 



FIG. 28. Skull of Quail. <?, quadrate bone. 



remain have few joints and are partly united. In the hind 

 limb the fibula is short, but especially noticeable is the 

 great lengthening of two of the ankle-bones, the result being 

 that the heel is elevated some distance from the ground. 



Birds are grouped in three divisions or subclasses, the 

 first two of which are extinct; the third contains the ten 

 thousand known species of living forms. 



CLASS I. SAURUR^; (Tailed Birds). 



These forms, found fossil in the lithographic stone of 

 Bavaria, had tails of extreme length, the feathers being 

 arranged on either side of the long tail vertebrae; and they 

 had teeth in the jaws. Only two specimens are known, the 



