MAMMALIA. 



539 



cartilage, it probably represents the clavicle and precoracoid 

 joined in one. Its distal end forms an attachment for the 

 humerus and it is also joined by a ligament to the scapula. 

 The scapula is long and narrow and assists, as usual, in 

 bearing the humerus. The bony connection of "clavicle," 

 episternum, ribs and vertebral column, assisted by the 

 scapula, forms a solid fulcrum for the fore-limb. The 

 humerus is quite unique. Short and stout, it is expanded 

 into lateral crests and processes. The radius and ulna are 

 also short and stout and the olecranon is long, increasing 

 the mechanical advantage of the extensor muscles. 



I'ig- 372.— Anterior View of Pectoral Girdle and Limb 

 OF THE Mole. 



Note the shortened limb, powerful clavicle and humerus and 

 broad scoop-like manus. 



The carpal bones are compact and the whole manus is 

 broad and flat. There are five short digits with strong 

 claws. Inside the first digit is a falciform bone which 

 some authorities regard as a prepollex or sixth digit What- 

 ever its homology, it assists greatly in adding to the 

 "expanse" of the hand. The movement of digging, like 

 those of swimming and flying, involves a great development 

 of the pectoral muscles ; and in correlation with this there 

 is a median keel or ridge on the sternum at their point of 

 origin (cf. bat and bird). All the above structural features 

 point to the burrowing function of the fore-limbs. With 

 regard to the forward extension of the episternum, and with it 



