278 THE ARM AND FORE-ARM. [CHAP. 



the humerus of the Manatee the bicipital groove is obsolete, 

 the two tuberosities coalescing, as in the Cetacea. In other 

 respects it resembles that of the Dugong. 



The two bones of the fore-arm are, in both genera, about 

 equally developed, and generally ankylose together at both 

 extremities. 



Order EDENTATA. In the Sloths the humerus is long 

 and straight, slender and cylindrical in the greater part, but 

 flattened and laterally expanded at the lower end. The 

 head is hemispherical, the tuberosities moderately developed, 

 and subequal in size, the deltoid ridge very indistinct. In 

 the Two-toed Sloths (Chol&pus) the humerus is shorter and 

 broader than in Brady pus, and has a large supracondylar 

 perforation, which is wanting in the latter genus. 



The radius and ulna somewhat recall those of the 

 Primates in their form, and they are capable of a con- 

 siderable amount of pronation and supination. The 

 olecranon process scarcely projects beyond the sigmoicl 

 articular surface. 



The humerus in all the remaining Edentates is stout and 

 broad, and remarkable for the great development of the 

 points of muscular attachment, as the tuberosities, deltoid, 

 and supinator ridges, and internal condyle. These all 

 reach their maximum of development in the Armadillos, 

 animals which make great use of their fore-limbs in 

 scratching and burrowing. The supracondylar foramen is 

 present in all. 



The radius and ulna are also well developed and 

 distinct in all, but with no great amount of motion 

 permitted between them. The olecranon is always long 

 and strong. 



Order MARSUPIALIA. In the burrowing Wombat (Phasco- 

 lomys) the humerus is stout, very broad at the distal end, 



