Chap. VIII.] THE SKELETON. 171 



proximal and distal row ; (c.) a distal row of five carpalia, num- 

 bered from the radial to the ulnar side ; (4) the metacarpus, com 

 posed of five metacarpalia articulated to the five carpalia ; and 

 (5), the five digits with articulating phalanges. 



In the rabbit the humerus has the form shown in dorsal view 

 in Fig. 55, C., where h. is the head, 1. 1. and g. i. the lesser and greater 

 tuberosity, sh. the shaft, o. f. the olecranon fossa, tr. the trochlea, 

 and cap. the capitellum. On the ventral aspect there is a well- 

 marked deltoid ridge. The radius and ulna have the form shown 

 in D. where ol. pr. is the olecranon, and si. c. is the sigmoid 

 cavity for articulation with the humerus. The two bones are 

 closely applied, and do not admit of that change of relative 

 position which gives us the power of rotating our hand and wrist. 

 In the carpus (E.) carpalia iv. and v. coalesce to form a single 

 bone (unciform), while the centrale is wedged in between carpalia 

 ii and iii. To the left of the ulnare in E. is seen a little bone 

 (shaded) ; this is the pisiform, hitherto regarded as an extrane- 

 ous bone developed in tendon. But the homologies of these 

 parts are being re-investigated, and some change of view (e.g. in 

 the nature of the pisiform) seems probable. Special names are 

 given to the bones of the mammalian carpus. In the proximal 

 row of the carpus the bones are (in E., reading from left to 

 right) pisiform, cuneiform, lunar, and scaphoid; in the distal row 

 they are unciform, magnum, centrale (wedged in from above), 

 trapezoid, and trapezium. 



In the fowl the humerus is a strong light bone. In the 

 ventral aspect the greater tuberosity is strongly marked ; in the 

 dorsal aspect, close to the lesser tuberosity, is an excavation 

 leading to the pneumatic foramen, by means of which air from 

 the interclavicular air-sac finds access to the shaft. The radius 

 and ulna (B.) do not call for especial notice. The manus is, 

 however, curiously modified in relation to flight. Of the carpus 

 only the ulnare and radiale are developed. The metacarpals i., 

 ii., iii., ankylose, and are peculiar in form. The others are 

 suppressed. Of the digits, one phalange of i., two of ii., and one 

 of iii., are developed. The rest are wanting in the adult. 



In the frog the humerus is short and curved, with a deltoid 



