296 SYSTEMATIC ZOOLOGY. 



to disappear, and in birds and mammals only parts of 

 the hyoid and first gill-bar remain in the adult, where 

 they are largely employed as supports for the tongue 

 and larynx (fig. 106). 



There are never more than two pairs of appendages in 

 the vertebrates. These are the fore and hind limbs. In 

 their skeletons these are much alike, and in each can be 

 recognized arches of bone (girdles) uniting the limb to the 

 trunk, and the skeleton of the limb proper. These girdles 

 are known respectively as the shoulder, or pectoral, and 

 the pelvic girdle. In the fishes the girdles are simple 

 arches, and the skeleton of the limbs is largely composed 

 of fin-rays to support the flattened swimming-organ. 



In those vertebrates which support the weight of the 

 body upon the limbs the appendicular skeleton is more 

 complicated. In its typical condition the shoulder-girdle 

 consists of three bones, which meet * to afford attachment 

 for the skeleton of the fore limb. One of these bones, the 

 shoulder-blade (scapula}, is dorsal. It never joins the 

 vertebra, but is united to the trunk by muscles and liga- 

 ments. The other two extend ventrally from the shoulder- 

 joint and meet the sternum. Of these the anterior is the 

 collar-bone (clavicle), the posterior the coracoid. 



In the pelvic girdle there are likewise three bones, which 

 at their point of junction give rise to the hip-joint. The 

 dorsal bone is the ilium, which articulates with the sacral 

 vertebrae (p. 292), while below are found the ischium and 

 pubis, the latter being the more anterior. Ischium and 

 pubis unite with their fellows of the opposite side, thus 

 completing the arch. 



In the pelvic girdle the parts mentioned are pretty con- 



* The clavicle frequently does not enter into the formation of the 

 shoulder-joint. 



