GC 



FIG. 96. AN APE'S PECTORAL GIRDLE AND ASSOCIATED PARTS. ] 



This characteristic part of a mammal's skeleton should be contrasted 

 with the corresponding parts in a bird (fig. 59). 



In the background are seen five of the seven neck vertebrae or cervical 

 vertebrae (CV). Hiding the thoracic or dorsal region of the backbone 

 is the segmented breastbone or sternum (ST), ending in a piece called 

 the xiphisternum (X). 



The two heads of the first rib are seen, the shorter tubercle and the 

 longer capitulum, articulating respectively with the transverse process 

 of the first thoracic vertebra and with the centra of the first and second. 

 The upper part of a rib (VR) is called the vertebral part; the lower 

 part (STR), which is cartilaginous in mammals (bony in birds), is called 

 the sternal part. 



Away behind are the broad scapulae, or shoulder-blades. In all mammals 

 except the oviparous Monotremes, the coracoids (so strong in birds) are 

 mere processes of the scapula (CP), separate in the young embryo, fused 

 on early in development. They share, however, in forming the glenoid 

 cavity (GC) in which the head of the humerus works. The strong clavicles, 

 or collar-bones (CL), are seen coming down to the top of the breast-bone. 



292 



