INTRODUCTORY 3 



to render the limb more efficient as an organ 

 of flight, the bones and musculature have under- 

 gone a change. The manus or hand has been 

 reduced by the disappearance of digits and 

 the consolidation of the metacarpus. The 

 clavicles are joined together, and the coracoid 

 is large to give firmness to the shoulder-girdle 

 in order that it may serve as a substantial 

 basis for the wing. Reduction in the manus, 

 combined with comparative simplicity in the 

 movements of the greater part of the limb, 

 has removed the necessity for large and strong 

 muscles in the forearm. The muscles of the 

 pectoral region, on the contrary, need to be 

 powerful, and an extensive surface for their 

 attachment is provided by the presence of a 

 deep keel on the sternum. In order that a 

 firm foundation may be given to the wing, 

 there has been extensive consolidation of the 

 vertebral column. 



With the capacity for flight must be associ- 

 ated certain peculiarities of the respiratory 

 organs. The air -passages within the lungs 

 are connected with large, thin-walled air-sacs 

 in the thorax and abdomen, these being con- 

 tinuous with air - containing cavities within 

 most of the bones of the skeleton. The lungs 



