XII 



PHYLUM CHORDATA 



497 



The radius and ulna are firmly fixed together so as to be 

 incapable of movement, but not actually ankylosed. The 

 radius articulates proximally with the humerus, distally with 

 the scaphoid and lunar bones (see below) of the carpus. The 

 ulna presents on the anterior aspect of its proximal end a deep 

 fossa, the greater sigmoid cavity p , for the trochlea of the humer- 

 us; the prominent process on the proximal side of this is the 

 olecranon process. Distally 

 it articulates with the 

 cuneiform. 



The carpal bones (Fig. 

 279), nine in number, are 

 all small bones of irregular 

 shape. Eight of these are 



arranged in two rows a 



' "" WPff f W 1 >Jk 



--U71C 



SC 



. tun 



*rp m ^UQSJSv- CUT* 

 trrj^qgg&jg^cenl 



proximal and a distal; 



the ninth, centrale (cent.\ 



lies between the two rows. 



The bones of the proximal 



row are taken in order 



from the inner to the 



outer side scaphoid (sc.), 



lunar (or semi-lunar} 



(/.), cuneiform (am.), 



and pisiform. Those of 



the distal row are reckoned in the same order, trapezium 



(trpm.\ trapezoid (trpz.), magnum (mag.\ and unciform 



(unc.). 



The five metacarpals are all small but relatively narrow 

 and elongated bones, the first being smaller than the rest. 

 Each of the five digits has three phalanges, except the first 

 which has only two. The distal (ungual) phalanges are 

 grooved dorsally for the attachment of the horny claw. 

 Man. Zool. v v 



TTiaa 



FIG. 279. Lepus cuniculus. Distal end 

 of fore-arm and carpus, dorsal view. 

 cent, centrale ; cun. cuneiform ; lien. 

 lunar ; mag. magnum ; rod. radius ; 

 sc. scaphoid ; trpm. trapezium ; trfz. 

 trapezoid ; uln. ulna ; unc. unciform ; 

 / V, bases of metacarpals. (After 

 Krause.) 



