82 RADIUS. CARPUS. 



round above, where it supports the supinator brevis muscle, and 

 marked by several shallow oblique grooves below, which afford attach- 

 ment to the extensor muscles of the thumb. The external surface is 

 rounded and convex, and marked by an oblique ridge, which extends 

 from the tuberosity to the styloid process at the lower extremity of 

 the bone. Upon the inner margin of the bone is a sharp and promi- 

 nent crest, which gives attachment to the interosseous membrane. 

 The lower extremity of the radius is broad and triangular, and pro- 

 vided with two articular surfaces ; one at the side of the bone, which 

 is concave to receive the rounded head of the ulna ; the other at the 

 extremity, and marked by a slight ridge into two facets, one exter- 

 nal and triangular, corresponding with the scaphoid ; the other square, 

 with the semilunar bone. Upon the outer side of the extremity is 

 a strong conical projection, the styloid process, which gives attachment 

 by its base to the tendon of the supinator longus, and by its apex to 

 the external lateral ligament of the wrist joint. The inner edge of 

 the articular surface affords attachment to the base of the inter-arti- 

 cular cartilage of the ulna. 



Immediately in front of the styloid process is a groove, which lodges 

 the tendons of the extensor ossis metacarpi pollicis, and extensor primi 

 internodii ; and behind the process a broader groove, for the tendons of 

 the extensor carpi radialia longior and brevior, and extensor aectmdi 

 -internodii ; behind this is a prominent ridge, and a deep and narrrow 

 groove, for the tendon o tke-^xtensor indicts ; and still farther back 

 part of a broad groove, completed by the ulna, for the tendons of the 

 extensor communis digitorum. ~ <fL*^**-* *-y-Vi 



Development. By three centres; one for the shaft, and one for each 

 extremity. Ossification commences in the shaft soon after the hu- 

 merus, and before that in the ulna. The inferior centre appears 

 during the second year, and the superior about the seventh. The 

 bone is perfected at twenty. 



Articulations. With/bwr bones; humerus, ulna, scaphoid, and 

 semilunar. 



Attachment of Muscles. To nine ; by the tuberosity to the biceps ; 

 by the oblique ridge to the supinator brevis, pronator radii teres, 

 flexor sublimis digitorum and pronator quadratus ; by the anterior 

 surface, to the flexor longus pollicis and pronator quadratus ; by the 

 posterior surface, to the extensor ossis metacarpi pollicis, and extensor 

 primi internodii ; and by the styloid process, to the supinator longus. 



CARPUS. The bones of the carpus are eight in number ; they are 

 arranged in two rows. In the first row, commencing from the radial 

 side, are the os scaphoides, semilunare, cuneiforme, pisiforme ; and in 

 the second row, in the same order, the os trapezium, trapezoides, os 

 magnum and unciforme. 



The SCAPHOID bone is named from bearing some resemblance to 

 the shape of a boat, being broad at one end, and narrowed like a prow 

 at the opposite, concave on one side, and convex upon the other. It 



