SKELETON OF THE DUCK TRIBE. 141 



figure to the trunk of these swimming-birds, which is 

 well adapted to their favorite medium and mode of loco- 

 motion. The bones of tlie wing or anterior extremity do 

 not present that extraordinary development which might 

 be expected from the powers of the member of which 

 they form the basis. The great expanse of the wing is 

 gained at the expense of the epidermoid system (quills 

 and feathers, like hairs and scales, are thickened epiderm), 

 and is not exclusively produced by folds of the skin re- 

 quiring elongated bones to support them, as in the flying- 

 fish, flying-lizards, and bats. The wing-bones of birds 

 are, however, both in their forms and modes of articula- 

 tion, highly characteristic of the powers and applications 

 of the muscular apparatus requisite for the due actions 

 of flight. The bones of the shoulder consist on each side 

 of a scapula, 51, a coracoid, 52, and a clavicle, 58, the 

 clavicles being, as a general rule in birds, confluent at 

 their median ends, and so forming a single bone called 

 "furculum," or ^'osfurcatorium;" this further modification 

 of the haemal arch in birds, repeating that of the pubis 

 and lower jaw in some other animals, having occasioned 

 an additional specific term in ornithotomy. The scapula, 

 51, is a long, narrow, flat sabre-shaped plate, expanded at 

 the humeral end, where it forms externally part of the 

 joint for the arm-bone called "glenoid cavity," and ex- 

 tended backwards nearly parallel with the vertebrae, as 

 far as the ilium, 62, in the swan, and reaching to the last 

 rib in the swift ; but it is much shorter in the birds in- 

 capable of flight. The coracoid is the strongest of the 

 bones of the scapular arch: it forms the anterior half of 

 the glenoid cavity, extends above this part to abut upon 

 the furculum, and is continued downwards below the 

 joint, expanding, to be fixed in the transverse groove at 



