THE RADIUS 



127 



and affords attachment to the jiexor imbliniis digitorum. The posterior border 

 begins at the back of the tuberosit}^ and extends to the middle tubercle on the 

 posterior aspect of the lower extremity. The anterior surface is bounded by the 

 anterior and interosseous borders. The upper tAvo-thircls is occupied by the flexor 

 longus polUcls, and a little less than the lower third by the lyronator quadratus. The 

 external surface lies between the anterior and posterior border.s. The upper third 

 affords insertion to the supinator brevis ; at its centre there is a rough, low, vertical 

 ridge for the pronator radii teres ; below this, the bone is smooth and overlapped ])v 

 the tendons of the extensores carpi radialis longior and brevior, and crossed by tlie 

 extensor ossis metacarpi poUicis and extensor primi internodii pollicis. The posterior 



Fig. V.\:\. — Ossification of the Radius and Ulna. 



I 



APPEARS AT TUf TENTH YEAR; FUSES AT THE 



SIXTEENTH YEAR 



APPEARS AT THE FIFTH YEAR; FUSES AT THE 

 SEVENTEENTH YEAR 



APPEARS AT THE FOURTH YEAR; FUSES AT THE 



EIGHTEENTH YEAR 

 APPEARS AT THE SECOND YEAR; FUSES AT THE 



TWENTIETH YEAR 



surface lies between the interosseous and posterior borders. The upper third gives 

 origin to the extensor ossis metacarpi and the extensor primi internodii pollicis, and 

 the lower third is covered by tendons. 



The lower extremity of the radius is quadrilateral; its carpal surface is articu- 

 lar and divided by a ridge into an inner quadrilateral portion, concave for articula- 

 tion with the semilunar bone; and an outer triangular portion, extending on to the 

 styloid process: this is concave to receive the superior surface of the scaphoid bone. 

 The inner side of the lower end presents the sigmoid cavity for the reception of 

 the rounded margin of the head of the ulna. The anterior sm-face is a raised 

 ridge to which the anterior ligament of the wrist-joint is attached. The outer 

 surface is represented by the styloid process, to the base of Avhich the siqmuttor 

 longus is inserted; and the tip of the process serves for the attachment of the 

 external lateral ligament of the wrist. It is also marked by a shallow furrow 



