604 BIRDS. 



tympanum to the inner ear extends the rod-like columella. 

 The lower jaw originally consists of four membrane bones 

 — dentary, splenial, angular, and surangular ; and one carti- 

 lage bone — the articular. The hyoid consists of a flat 

 "body," with anterior and posterior "horns," the latter 

 derived from the first branchial arch. 



The pectoral girdle consists of sabre-like scapulas extend- 

 ing dorsally over the ribs, of stout coracoids sloping ventrally 

 and articulating with the sternum, of the clavicles which are 

 united by the interclavicle to form the merrythought or fur- 

 cula. The opening left where the upper ends of the clavicles 

 touch the scapula and coracoid is called the foramen triosseum. 



The sternum bears a conspicuous keel, is produced 

 laterally and posteriorly into two xiphoid processes, and 



Fig. 264. — Side view of pelvis of cassowary. 

 //., Ilium ; fsc/t., ischium ; Pb., pubis ; Ac, acetabulum. 



bears articular surfaces for the coracoids anteriorly, for the 

 sternal ribs laterally. 



The skeleton of the wing includes the stout humerus, the 

 separate radius and ulna (the latter the larger), two free 

 carpals, a carpo-metacarpus of three metacarpals fused to 

 one another and to some carpal elements, and three digits 

 — the thumb with one joint, the first finger with two joints, 

 the second with one. In adaptation to flight, the wing of a 

 bird has much less flexibility of parts than the arm of a 

 Mammal. The radius and ulna do not move upon each other. 



The pelvic girdle consists of dorsal ilia fused to the 

 complex sacral region, of ischia sloping backwards, and of 

 pubes running parallel to the ischia. The incomplete 

 ossification of the acetabulum and the absence of ventral 

 symphyses are noteworthy. 



