66 ANATOMY OF VERTEBRATES. 



each other, but are severally anchylosed with the coracoid and 

 scapula, so as to form with them one bone on either side. In the 

 Frigate-bird the clavicles coalesce with the coracoids, as well as 

 with each other and Avith the sternum. In almost every other 

 species of bird the scapula, coracoid, and clavicle are moveably 

 articulated to each other throughout life. In Rliea and Casuarius 

 the acromial element or clavicle is anchylosed with, or rather is 

 a continuous ossification from, the scapula ; but the coracoid bone 

 is free, a condition which the bones of the shoulder present in 

 the Chelonian Reptiles (vol. i. p. 172, fig. 106). 



In the Emeu {Dromaius) it is interesting to observe that each 

 clavicle commences by a distinct ossification, and long continues 

 separate from the scapula ; it does not reach the sternum, but holds 

 the same relative situation as the continuous acromial or clavicular 

 process of the scapula in the other Struthious birds. The cla- 

 vicles are distinct from each other and from the coracoid in some 

 Ground Parrots and carpophagous Doves (^Columha galeata, e. g.). 



The scapula, fig. 19, 5i, is broader and flatter in the Penguins 

 (Aptenodytes) than in other birds. In the rest of the class it is a 

 long and narrow sabre-shaped bone, 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, acro- 

 mially, to meet the clavicle, while it is strongly attached in the 

 remainder of its anterior surface to the coracoid. The blade of 

 the scapula may expand towards the free end {^Gallin(E)\ and 

 this may be obliquely truncate {Gallince), or taper to a point 

 (most Avcs), Avhich point maybe decurved {Columha) ; it is rarely 

 obtuse ( Tetrao, Apteryx, Dinornis). The position of the scapula 

 is longitudinal, being extended backward from the shoulder, 

 parallel to the vertebral column, towards which, however, it 

 presents a slight convexity. In some birds it extends over the 

 ribs to, or even above, the fore part of the ilium ; while in the 

 Emeu and Apteryx it crosses over two ribs only. In the Hum- 

 ming-bird {Trochilus), fig. 19, t, its posterior third is bent down- 

 ward at a slight angle. In birds where the scapula is pneumatic, 

 the perforations are at the base of the acromial process. 



The coracoid, fig. 18, u, figs. 16, 19, 20, 52, is the strongest of 

 the bones composing the scapular arch : its expanded extremity is 

 securely lodged below in the transverse groove at the anterior 

 part of the sternum, from which it extends upward, outward, and 

 forward, but sometimes almost vertically, to the shoulder-joint, 

 wliere it is articulated usually at an acute angle with the scapula 



