284 ZOOLOGY. 



numerous processes for the insertion of muscl. - a^Ut in these 

 motions. 



On the other hand, in almost all birds the vertebrae of the 

 back are nearly tixrd or immovable, and this, no doubt, is to 

 enable the wings to find in this part of the trunk a point of 

 support. In general, they are consolidated or united into 

 one, but in birtu which do not fly, as the ostrich and cassowary 

 (Fig. 138), they remain distinct, and preserve their mobility. 

 The lumbar and sacral vertebrae unite into one ; the coccygeal 

 are small and moveable, the last generally larger than the 

 others, and is raised into a crest. It supports the large fea- 

 thers of the tail (Fig. 222). 



430. The ribs of birds show some peculiarities tending 

 to give solidity to the chest or thorax. The cartilage uniting 

 the rib to the sternum is osseous in the bird, and each rib 

 has a process, which, running backwards over the other rib, 

 so overlaps them that all the ribs support each other. 



But the most remarkable part of the skeleton of the thorax 

 is the sternum (Fig. 224), which, giving attachment to the 

 muscles used in flight, assumes an extraordinary develop- 

 ment, enclosing not only the thorax, but a large part of the 

 abdomen. In the cassowary and ostrich (Fig. 138) which do 

 not fly, the sternum has no external crest, and the wings aiv 

 rudimentary ; but this exists in other birds, and is called the 

 keel or brechet (b, Fig. 224) ; by multiplying the muscular 

 attachments favourably, it gives more force to the depressor 

 muscles of the wings. 



431. The bones of the shoulder are in like manner 

 favourable for the action of the wings. The scapula (o) is 

 narrow and elongated, and placed in the axis of the spine ; it 

 rests on the sternum not only by the clavicles called four- 

 chette or merrythought (/), but also by the clavicles called 

 coracoid (c), so termed because they seem to be prolongations 

 of the coracoid process in man. The clavicles called fourchetto 

 unite generally below with each other, and are attached to the 

 crest of the sternum, and, together with the powerful coracoid 

 clavicles offer a strong point d'appui for the wings to act on, 

 and these structures are proportioned to the power of flight of 

 the bird. Thus, in some of the terrestrial paroquets of Aus- 

 tralia, these bones are reduced to an almost rudimentary state ; 

 in the cassowary and American ostrich the fourchette is repre- 

 sented by two small stylets ; in the African ostrich and 

 the toucan they nearly reach the sternum, but do not unite 



