22 



ANATOMY OF THE DOMESTIC FOWL 



neck; the plates of the corneal margin of the sclerotic tunic of the 

 eye; and the stapes of the ear. Ossification in birds at the attach- 

 ments of the semi-lunar valves of the aorta and of the pulmonary 

 artery has been reported by Owen. 



The bony structure is compact, and the bones contain a greater 

 proportion of phosphate of lime than do the osseous structures 

 of mammals. Especially is this the case in those parts of the 

 skeleton which are permeated by air. 



The bodies of birds contain many air reservoirs to make them 

 light that flying may be more easy. Many bones have their weight 

 in proportion to size and strength thus greatly reduced. In very 

 young birds the cavities of bones contain, instead of air spaces, 

 loosely arranged red marrow, which is in most bones later absorbed. 



