THE ENGLISH SPARROW 383 



runs up to the vertebrae and the other down to the breastbone. 

 The two halves of the girdle thus formed are kept apart 

 by a bone that serves as a spring, the so-called wishbone 

 (Fig. 352, fur). While the shoulder girdle is thus character- 

 ized by a high degree of elasticity as befits its important work 

 of supporting the strokes of the wing, the pelvic girdle, on the 

 other hand, consists of a pair of bones rigidly fastened to the 

 immovable sacral vertebrae. 



The skeleton of the wing consists of a single bone in the 

 upper arm, two bones in the forearm, and rudiments of three 

 fingers in the hand. The skeleton of the leg consists of a single 

 bone (femur) in the upper leg, two bones (tibia and fibula) 

 in the lower leg, a kneepan (or patella) at the joint between 

 the upper and lower leg, and a foot consisting of four digits 

 which are grown together in what corresponds to the sole of 

 the foot in man (the shank of the bird's leg), but are separate 

 in the toes. 



Organs of nutrition in the pigeon are much more com- 

 plex than in the lower classes of vertebrates (Fig. 354). From 

 the toothless mouth, with its long tongue, the long gullet leads 

 through the neck to enlarge into a capacious crop lying just 

 in front of the wishbone. Here the food, which consists 

 chiefly of grain, is thoroughly soaked and softened. Thence 

 it passes by a continuation of the gullet to the stomach, which, 

 as in most birds, consists of two parts ; the first, which is 

 glandular; the second, or gizzard, which is muscular. In the 

 first part the grain is further softened and treated by the se- 

 cretions of the glands ; in the second it is mechanically treated, 

 being crushed and ground by aid of small stones that have been 

 swallowed by the bird. From the gizzard leads the intestine. 

 In its anterior part the digestive processes are active, and it 



