ANATOMY OF MEGAPTERA LONGIMANA. 49 



sheath, along the radial border of the interosseous space, is a 

 large artery, continued along the radial border of the common 

 tendon. 



Common Tendon. The tendons of the two flexors unite in a 

 common triangular expansion, the bulk of which appears to 

 exceed that of the two tendons which form it. From this four 

 tendons proceed, of about equal size, to the four digits. Breadth 

 of the tendons along proximal half of the digits, 1 to 1 \ inch ; 

 on distal half, broader ; on the cartilages, 2 inches. They go to 

 the ends of the digits. They have a fibrous covering, but not 

 regularly formed thecse and have no synovial covering, only 

 areolar tissue between. Their function must be ligamentous, 

 with traction exerted on them by the muscles. 



The greater size of the radial flexor than of the ulnar flexor 

 in Megaptera, in contrast with their proportions in B. musculus, 

 is interesting as in adaptation to the greater size of digit II. in 

 Megaptera. Although the two tendons unite in a common 

 expansion, the radial flexor will exert its traction on the radial 

 side. 



Extensor communis digitorum. Fleshy belly 18 inches in 

 length, greatest breadth 1J inch, being same length as in B. 

 musculus, but only half the breadth. Tendon | inch in breadth ; 

 in B. musculus was 1J inch. Is about size of human tendo 

 Achillis. Forms large triangular expansion on distal half of 

 carpus, which gives off four tendons at the proximal ends of the 

 metacarpal bones. The division in B. musculus was earlier, at 

 about the middle of the carpus. Tendon to digit III. the 

 largest, that to digit V. the smallest. At middle of digit III. 

 the tendon is twice the bulk of the entire tendon in the fore-arm ; 

 breadth 2 inches, thickness \ inch. The tendons have attach- 

 ments to all the bones and joints. 



Function, Here, then, we see in the great paddle of Megap- 

 tera the same muscles not half the size they have in the much 

 smaller paddle of B. musculus, illustrating their rudimentary 

 condition. The great increase of the bulk of the tendons on 

 the digits is an illustration of their mainly ligamentous func- 

 tion. The traction exerted on them by the muscles will give 

 some additional resistance on both aspects. 



