SKELETON OF THE WILD DUCK. THE STERNUM. 321 



ribs which are without uncinate processes, become progressively 

 more slender, and in the eighth the tubercular processes are lost. 

 The sternal portions of the ribs are imperfectly ossified 

 pieces, short and comparatively thick in the case of the anterior 

 ribs, longer and more slender in the case of the posterior ribs. 



THE STERNUM 1 . 



The sternum or breast bone is exceedingly large in the 

 Duck, as in all birds, and projects back far beyond the thorax over 

 much of the anterior part of the abdomen. It is an irregularly 

 oblong plate of bone, abruptly truncated behind, somewhat 

 concave dorsally, and drawn out ventrally into a prominent keel, 

 the carina, which projects for some distance forwards beyond 

 the body of the sternum, and tapers off gradually behind. 

 The point where the carina joins the body of the sternum is at 

 the anterior end drawn out into a small process, the rostrum 2 . 

 Just dorso-lateral to this are a pair of deep grooves, the 

 coracoid grooves, with which the coracoids articulate. 



The sides of the sternum are drawn out in front into a 

 pair of short blunt costal processes ; and just behind these 

 are a series of seven surfaces with which the ends of the 

 sternal ribs articulate. Immediately behind these surfaces 

 the sides are produced into a pair of long backwardly-pro- 

 jecting xiphoid processes which nearly meet processes from 

 the posterior end of the sternum. 



2. THE APPENDICULAR SKELETON. 



This consists of the skeleton of the anterior and posterior 

 limbs and of their respective girdles. 



A. THE PECTORAL GIRDLE \ 



The pectoral girdle in almost all birds is strongly constructed 

 and firmly united to the sternum. It consists of three bones, 

 a dorsal element, the scapula, a posterior ventral element, the 

 coracoid, and an anterior ventral element, the clavicle. 



1 Cp. fig. 63. 



2 Often called the manubrium, but not homologous with the manu- 

 brium of the mammalian sternum. 



R. 21 



