VERTEBRATA. 133 



In those vertebrates which support the weight of the body 

 upon the limbs the appendicular skeleton is more compli- 

 cated. 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 ver- 

 tebrae, but is united to the trunk by muscles and ligaments. 



Fro. 60. Diagram of fore and hind limbs of a terrestrial vertebrate, with 

 one half of their girdles, c, carpus ; cl, clavicle ; co, coracoid ; f, fibula ; 

 e, femur ; 7j, humerus ; il, ilium ; is, ischium ; me, metacarpus ; mt, meta- 

 tarsus ; p, pubis ; r, radius ; s, scapula ; t, tarsus ; u (in upper) ulna, (in 

 lower) tibia ; 1 5, digits, each composed of phalanges. " 



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 

 vertebras (p. 129), 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- 

 stant, but in the shoulder-girdle other bones may be added, 



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

 shoulder- joint. 



