INTRODUCTION. yii 



Of the osteology of birds much -will not be said. In the com- 

 position of the frame of the body, birds may be said to have false 

 ribs anterior and posterior to the true ribs. These cover nearly 

 the whole short body or trunk, terminate anteriorly in a single articu- 

 lation with the sternal ribs, and pass forwards to be fixed on the 

 sternal appendices on the middle of the trunk. The false ribs 

 do not at all touch the sternum (TT) or breast bone. In the act of 

 respiration the sternum in birds plays a very important part. It is one 

 of the most remarkable and characteristic bones of the skeleton first, 

 for its great development ; next, for the extent to which it covers the 

 trunk, enveloping, as it does, all the internal organs, and by the 

 median carina in front, giving it solidity, as well as strength and 

 power to the pectoral muscles, the limits of attachment of which latter 

 are marked on the external surface. The surface presented by the 

 sternum or breast-bone bears the permanent and powerful muscles of 

 the humerus; the trunk is solid, and the scapula, situated as it is 

 along the side of the vertebral column, gives attachment to the 

 powerful muscles of flight, while the chief support and means of 

 resistance is the coracoid-bone (c). The sternum is not of one shape 

 or form throughout the class, but is variable in consonance with the 

 habits of the different orders, and these different shapes, forms, 

 and varieties of appearance lend considerable aid to the anatomist 

 and systematist in working out perplexed affinities. In ducks and 

 geese the posterior margin is replaced by membrane. In gallinaceous 

 birds it terminates in narrow, separate bones ; this is on account of 

 their habit of running and feeding on the ground ; while the high- 

 flying rapacious birds have it solidly anchylosed and ossified. There 

 are no parts of animals which vary so much in form and struc- 

 ture as the atlantal and sacral (f) extremities; the parts remotest 

 from the centre of the skeleton are the most mutable in form ; and 

 the organs of progressive motion conform most to the medium in 

 which animals reside. These parts vary so much in the same class 

 of animals, that we might almost be induced to imagine that in 

 organs so different as the human hand, and the fin of the porpoise 

 or the wing of the bat, or the forefoot of the mole, all unity of compo- 

 sition was lost; and in passing to different classes we should scarcely 

 expect to iind the bume element of structure which compose the fin 



