136 SKELETON OF BIRDS. 



attacliecl, lie will have a segment of the skeleton, answer- 

 ing to that figured in Fig. 5, p. 28. 



The cut surfaces will demonstrate the light cellulosity 

 of the divided bones. The following letters indicate the 

 elements of such modified vertebras of the thorax : ?/, cen- 

 trum, with its hyapophysis; 79, parapophysis ; c?, diapo- 

 physis; ?i, neural arch and rudimental spine; pl^ pleura- 

 pophysis ; /i, haemapophysis ; hs^ haomal spine. The tend- 

 ency of individual elements and bones to coalesce in birds 

 has already been illustrated in the cranium ; it is shown, 

 in most birds of flight, not only by the confluence of the 

 centrum with the neural arch, but by that of several con- 

 secutive centrums and arches into a single bone, in the 

 ample chest. In like manner the haemal spines, which 

 continue distinct in many vertebrata, have here coalesced 

 into a single bone, Avhich articulates on each side with 

 the ha3mapophyses of several vertebras. These coalesced 

 spines are also much developed in breadth, and send 

 down, from the middle of their under surface, a longi- 

 tudinal crest or keel. This modification relates to the 

 extension of the surface for the origin of the great mus- 

 cles of flight, and renders the " sternum," as the coalesced 

 series of haemal spines is called, one of the most charac- 

 teristic parts of the skeleton of the bird. Ossification 

 extends from the neural arches into the tendons of the 

 vertebral muscles, and such bone-tendons, both here and 

 in other parts of the body, as the legs, are also character- 

 istic of birds. The scapula (Fig. 24), 51, is long and 

 slender, as in the chelonia, but is more compressed and 

 sabre-shaped. The coracoid, 52, as a general rule, is a 

 distinct bone, movably articulated to the scapula at one 

 end and to the sternum at the other. Its broad sternal 

 end here articulates by a kind of gomphosis with a deep 



