THE FRAMEWORK OF THE BODY 45 



two pairs have their front cartilage ends unattached, and 

 are therefore called floating ribs. All the ribs have a 

 downward slope, their front ends being lower than the 

 hinder ones. This per- 

 mits of a considerable 

 enlargement in the size 

 of the cavity of the 

 thorax, or chest, when, 

 by the contraction of 

 the muscles of the 

 chest, the front ends 

 of the ribs are raised. 

 The object of this will 

 be shown later. 



45. The Sternum, or 

 breastbone (Figs. 27 

 and 33), supports the 

 forward ends of the 

 ribs (with the excep- 

 tion of the two lowest, 

 or floating ribs) by 



means of the costal pig . 33 ._ skeleton of thorax> showing ribs> 

 cartilages, which give costal cartilages, sternum, and some of the 

 more freedom of move- thoracic vertebr - 

 ment than would be possible were the bones solid to the 

 end. The sternum is composed, in the adult, of three 

 pieces, the lowest being of cartilage. 



46. The Appendicular Skeleton is composed of the pectoral 

 girdle, the pelvic girdle, and the bones of the limbs. 



47. The Pectoral Girdle (Fig. 27) consists of four bones, 

 two on each side, the scapula and the clavicle. The 

 scapula, or shoulder blade, is a triangular, nearly flat 

 bone lying at the back of the shoulder and not attached 



