284 



AVES. 



in the latter there may be observed slight indi- 

 cations of the two ordinary posterior fissures. 



The ossification of the perfect sternum of 

 the Bird commences from five centres, a 

 middle one which supports the keel, termed by 

 by Geoffrey St. Hilaire the entosternal (a, fig. 

 129); two anterior lateral pieces, the hyoster- 

 nals (b, bj Jig. 1 29), and two posterior lateral 

 pieces, the hyposternals (c c, fig. 129). The 

 posterior cartilaginous appendages he terms 

 xiphi-sternals (g g,fg. 129, 130). If to these 

 be added the two portions or episternals of 

 which he supposes the manubrial process to 

 be composed, then nine elements may be 

 reckoned to enter into the composition of the 



the coracoid element has been err neously re- 

 garded as the clavicle, in consequence of its 

 being moveably articulated with the scapular 

 piece. In the Emeu ( Dromaius) it is interesting 

 to observe that the clavicle commences by a dis- 

 tinct ossification, and long continues separate ; 

 it does not reach the sternum, but holds the 

 same relative situation as the continuous acro- 

 mial or clavicular process of the scapula in the 

 other Struthious birds. 



The scapula (t, fig. 125, A, fig. 130) is 

 most readily recognised as such, in the Pen- 

 guins of the genus Aptenodytes, where it is 

 broader and flatter than in any other bird : in 

 these, however, it is of considerable length in 



Fig. 130. 



sternum; but, hitherto, we have only met 

 with a single ossific centre in the manubrial 

 process. Where the keel is absent, as in the 

 Cursores, the entosternal piece appears to be 

 wanting, and the ossification of the sternum 

 here radiates from lateral centres only. 



Of the anterior extremity. The bones of 

 the anterior extremity do not present that ex- 

 traordinary development in the bird that might 

 be expected from the powers of the member 

 of which they are the basis. The great expanse 

 of the wing is here gained at the expense of the 

 epidermoid system, and not exclusively pro- 

 duced by folds of the skin requiring elongated 

 bones to support them, as in the Bats, Dragons, 

 and Flying-fish. The wing-bones are, however, 

 both in their forms and modes of articulation, 

 highly characteristic of the powers and appli- 

 cation of the muscular apparatus requisite for 

 their due actions in flight. 



The bones of the shoulder consist, on each 

 side, of a scapula (h, fig. 1 30), a coracoid 

 bone ( i), and a clavicle (k), the clavicles 

 being mostly anchylosed together at their mesial 

 extremities, constitute a single bone, which, from 

 its peculiar form, is termed the os furcator ium 

 or furculum. In the Ostrich the two clavicles 

 are distinct from each other, but are severally 

 anchylosed with the coracoid and scapula, so as 

 to form one bone on either side. In almost 

 every other species of bird the scapula, coracoid, 

 and clavicle remain separate or moveably articu- 

 lated throughout life. In the American Ostrich 

 (Rhea) and Java Cassowary (Casuarius) 

 the acromial element or clavicle is anchylosed 

 with, or rather is a continuous ossification from, 

 the scapula ; but the coracoid bone is free ; 

 and this condition is worthy of notice as it 

 i's precisely that which the bones of the shoul- 

 der present in the Chelonian Reptiles; where 



proportion to its breadth, and does not exhibit 

 any trace of spinous process. In the rest of the 

 class it is a simple narrow elongated bony 

 lamina, increasing in thickness as it approaches 

 the joint of the shoulder ; there it is extended 

 in the transverse direction, forming externally 

 the posterior half of the glenoid cavity, and being 

 internally more or less produced to meet the 

 clavicle, while it is strongly attached in the re- 

 mainder of its anterior surface to the coracoid 

 bone. The position of the scapula is longitudi- 

 nal,being extended backwards from the shoulder, 

 parallel to the vertebral column, towards which, 

 however, it, in general, presents a slight convex- 

 ity. In birds of strong powers of flight, as in the 

 Swift, (Cypselus,) it reaches to the last rib, 

 while in the Emeu, on the contrary, it extends 

 over two ribs only. In the Humming-bird 

 (Trochilus) its posterior third is bent down- 

 wards at a slight angle. 



The coracoid (u,fig.\ 25, i,fgs. 129, 130), or 

 posterior clavicle, is always the strongest of 

 the bones composing the scapular arch : its ex- 

 panded extremity is securely lodged below 

 in the transverse groove at the anterior part of 

 the sternum, from which it extends upwards, 

 outwards, and forwards, but frequently al- 

 most in the vertical position to the shoulder - 

 joint, where it is united at an acute angle with 

 the scapula and clavicle. It thus forms the 



