Aves. 211 



front angle of the wing, or ''bend of the wing," as it is 

 called, corresponds to our wrist ; but the hand is sharply 

 bent back upon the forearm when the wing is folded, a posi- 

 tion we cannot assume. When the wing is folded, the arm, 

 forearm, and hand lie alongside of each other like this, z. 

 Further, the hand is reduced to two fingers, bound together, 

 and the thumb, which every one has seen in the plucked 

 fowl. The thumb, with its feathers, is called the false wing. 

 The feathers borne on the hand are called primaries, and 

 those supported by the forearm are the secondaries. In 

 some cases a few of the inner feathers of the forearm are 

 called tertiaries. The wing is concave on the inside, mak- 

 ing it fit the body closely when the wing is folded. 



The Flying Muscles. To use such a wing effectively as 

 an air paddle, it is evidenj: that there must be very strong 

 muscles. These we find in the breast. The bulk of the 

 breast is made up of two powerful muscles, which cover 

 nearly the whole of the ventral surface of the body. To 

 support these large muscles, and supply a basis for their 

 attachment so they can work, it is equally clear that a con- 

 siderable extent of bone is also a necessity ; hence the large 

 breastbone. Not only is the breastbone very large, but 

 along its middle line is a high ridge, the keel. Lying 

 between the body of the breastbone and the keel, and 

 attached to both, there is on each side the large pectoral 

 muscle, the two together constituting about one fifth of the 

 entire weight of the body. At the anterior end, each pec- 

 toral muscle narrows into a tendon, which is attached (in- 

 serted) to the bone of the upper arm (humerus). By the 

 shortening of this muscle the wing is pulled downward. 

 Two points must now be kept in mind: (i) the wing is 

 concave beneath, which enables it to " catch " the air ; 

 (2) the wider side of the vane of each quill is on the under 



