ELEMENTARY SKETCH OF THE OSTEOLOGY OF BIRDS, 19 



fio-s. 1 and 2 ; IV, fig. 6, cor.), aud the furculum* or clavicles 

 {ibid. fu.). The scapula (sc.) corresponds to the shoulder-blade 

 or scapula of mammals, but in place of being a broad and ex- 

 panded plate with a median ridge, as is generally the case in 

 that class, is a compressed sabre-shaped bone, in length gener- 

 ally proportional to the power of flight, and generally placed 

 parallel with the vertebral column. There is no bone in birds 

 corresponding to the supra-scapulaf of reptiles. The coraeoid 

 (cor.) which corresponds to the coraeoid process^ of the hio-her 

 mammalian scapula, in birds, as in reptiles and the lowest mam- 

 mals, always exists as a distinct bone. The distal end of the 

 coraeoid is received into the groove of the sternum, which we 

 have already referred to, when describing that bone, while the 

 proximal end articulates with the scapula to form the o-lenoid 

 cavity for the reception of the head of the humerus. There is 

 never any notch or fontanelle in the coraeoid of the bird, as is so 

 often the case in reptiles. 



The relative position of the scapula and coraeoid afford au 

 important pcint of distinction between the Ratitas and the Oari- 

 nat£e. In the former group the long axis of that part of the 

 scapula which lies near the glenoid cavity is parallel to, or conti- 

 nuous with, that of the coraeoid, and the two bones are always 

 anchylosed together. In the Carinatse, on the other hand, the 

 long axis of the scapula nearly always forms an acute angle with 

 that of the coraeoid, though in the Dodo, and one or two other 

 birds, this angle is slightly obtuse. An ossification of the tendons 

 above the scapula frequently occurs in many of the Picarise and 

 Passeres which has been somewhat inappropriately named scapula 

 accessoria. 



The third bone of the avian shoulder-girdle is the furculum or 

 '' merrj^-thought" (fu.), which corresponds to the united clavi- 

 cles of mammals and reptiles. In most birds the furculum 

 forms one continuous bone, but occasionally, as in some Parrots, 

 Owls and Pigeons (pi. Ill, fig. 1), the two clavicles always 

 remain distinct. In other cases, as in T'acAj/joe^es (pi. Ill, fig. 2) 

 anchylosis extends down to the other elements of the shoulder- 

 girdle, and the furculum becomes immoveably united with the 

 rostrum of the carina of the sternum. In Opistkoeomus, the 

 furculum becomes united both with the carina of the sternum and 

 with the coracoids. In the Passerine birds (pi. I., fu.) the sternal 

 extremity of the furculum usually developes a large flat vertical 



* Furculum, a little fork, applied to the united clavicles or collar-bones of birds. 

 The word clavicle is derived from the diminution of clavis a key, from some supposed 

 resemblance of the human collar-bone to that instrument. 



f Supra-scapula, supra above, and scapula. 



X The coraeoid process in all mammalia ossifies from a centre quite distinct from 

 that of the scapula, 



