SKELETON AND TEETH 



75 



the anteaters and the extinct f ground-sloths, these sternal ribs, 

 at their lower ends, are provided with head and tubercle, for 

 articulation with the sternum. 



The sternum, or breast-bone, is made up of a niunber of 

 distinct segments, usually broad and flat, but often cyUndrical, 

 which may unite, but far more commonly remain separate 

 throughout hfe. The number, size and form of these segments 

 often give useful characters in 

 classification. The first seg- 

 ment, or manubrium, has quite 

 a different shape from the suc- 

 ceeding ones and is consider- 

 ably longer. 



II. The appendicular 

 skeleton consists of the limb- 

 girdles and the bones of the 

 limbs and feet. The limb- 

 girdles are the means of at- 

 taching the movable Umbs to 

 the body, so as to combine 

 the necessary mobility with 

 strength. The anterior, or 

 shoulder-girdle, has no direct 

 articulation with the vertebral 

 column, but is held in place by 

 muscles; it is made up of 

 the shoulder-blade and collar- 

 bone, though very many mam- 

 mals have lost the latter. 



The shoulder-blade, or Fig. 19. — sternum and rib-cartilages of 

 - . , 1 j.i_- 1 J. Wolf, lower side. P.S., manubrium. 



scapula, IS a broad, thm, plate- ^^ aphutemum. 

 like bone, which contracts be- 

 low to a much narrower neck, ending in a concave articular 

 surface, the glenoid cavity, for the head of the upper arm-bone, 

 the two together making the shoulder-joint. On the outer side 



