164 THE VERTEBRATE SKELETON. 



B. THE ANTERIOR LIMB. 



This is divisible into three parts, the upper arm or 

 brachium, the fore-arm or antibrachium, and the maims. 



All the larger bones have their ends formed by prominent 

 epiphyses which do not unite with the shaft till late in life. 

 Their articulating surfaces are covered by hyaline cartilage. 



In the upper arm there is a single bone, the humerus. 



This has a more or less cylindrical shaft and articulates by 

 a prominent rounded head with the glenoid cavity. The 

 distal end shows a large rounded swelling on either side of 

 which is a condylar ridge, the inner or postaxial one being 

 the larger. A prominent deltoid ridge runs along the 

 proximal half of the anterior surface, and in the male frog a 

 second equally prominent ridge runs along the distal half of 

 the posterior surface. 



The fore-arm consists of two bones, the radius and ulna, 

 united together and forming the radio-ulna. The two bones 

 are quite fused at their proximal ends where they form a 

 deep cup which articulates with the distal end of the humerus, 

 and is drawn out into a rather prominent backwardly-pro- 

 jecting olecranon process, which ossifies from a centre 

 distinct from that of the shaft. The distal end is distinctly 

 divided by a groove into an anterior radial and a posterior 

 ulnar portion. 



The manus consists of two parts, the wrist or carpus 

 and the hand. 



The carpus 1 consists of six small bones arranged in two 

 rows. The three bones of the proximal row are the ulnare, 

 radiale and centrale. The ulnare and radiale are about 

 equal in size and articulate regularly with the radio-ulna. The 

 centrale is pushed out of its normal position and lies partly on 

 the pre-axial side, partly in front of the radiale. Of the three 

 bones of the distal row the two pre-axial ones, carpalia 1 and 

 2, are small; carpale 2 articulates with the second metacarpal, 

 1 See G. B. Howes and W. Ridewood, P. Z. S., 1888, p. 141. * 



