282 ZOOLOGY. 



of the bones are different, and, cceteris paribus, their bones 

 are much lighter than those of mammals, being more or less 

 filled with air. 



The head of birds (Fig. 223) is generally small ; in the 

 young bird the cranium is composed of the same number of 

 bones as in mammals, but they unite very early together, and 

 the sutures disappear. The face is in a great measure formed 



Sacrum. Scapula. Huraerus. 



Coccyx. 



Clavicle. 



._ . ._ - Storm m. 



Tibia. - 



Tarsus 



Fig. 222. Skeleton of the Goeland. 



of the jaws, which are much elongated, and being chiefly em- 

 ployed by the bird as instruments of prehension, vary exceed- 

 ingly in their character, according to the nature of the bird, the 

 food it lives on, and the prey it attacks. The superior man- 

 dible is so articulated with the cranium as to admit of motion in 

 the cranium, independent of the lower jaw, which never occurs 



