Metazoa Ran a. 305 



delicate rod-like bones, the clavicles. Attached to the outer 

 ends of the clavicle and coracoid of either side is a broad 

 flat bone, the scapula, also tipped by a plate of cartilage 

 known as the supra-scapula ; while in the middle line and in 

 front of the inner union of the clavicles there lies a 

 small osseous rod, the omo-sternum, continued forward 

 as a delicate cartilaginous plate. The six bones above 

 referred to as forming the essential elements of the pectoral 

 girdle are the two clavicles, two coracoids, and the two sca- 

 pulae, which form a half-circle with the cartilaginous supra- 

 scapulse arching over the back. At the junction of the 

 coracoid and scapula there is a circular depression, or glenoid 

 cavity, into which the upper end of the fore-limb fits. 



A typical fore-limb consists of three parts : the arm, 

 composed of one bone, the humerus ; the fore-arm, of 

 two bones jointed to the lower end of the humerus, the 

 ulna externally, and the radius internally ; and a hand, 

 composed of many bones, forming proximally the wrist and 

 distally the fingers, or digits. Typically, the wrist, or carpus, 

 consists of an ulnare articulating with the distal end of 

 the ulna, a radiale articulating with the distal end of the 

 radius, and a small intermediate bone, the intermedium. In 

 front of the intermedium is a larger nodule, the centrale, and 

 beyond it five small bones, the carpals. To these five 

 carpals are articulated the five jointed digits, each made up 

 of a metacarpal and several phalanges. In the frog con- 

 siderable modification has taken place. In the first instance 

 the radius and ulna have fused to form one bone, though the 

 distinction is still visible at the extremities, while the nine 

 bones of the typical carpus has been reduced to six and the 

 first digit is rudimentary. 



Pelvic girdle and hind-limb. In the pelvic girdle there 

 is nothing corresponding to the sternum, though the other 

 elements of the pectoral girdle are represented. The scapula 

 is represented by a long curved bone on either side, the 

 ilium, placed dorsally and having its free end attached to 



