RADIUS. 139 



insertion of the tendon of the Biceps muscle, and an anterior smooth portion, on 

 which a bursa is interposed between the tendon and the bone. 



The Shaft of the bone is prismoid in form, narrower above than below, and 

 slightly curved, so as to be convex outwards. It presents three surfaces, separated 

 by three borders. 



The anterior border extends from the lower part of the tuberosity above, to the 

 anterior part of the base of the styloid process below. It separates the anterior 

 from the external surface. Its upper third is very prominent ; and, from its 

 oblique direction, downwards and outwards, has received the name of the oblique 

 line of the radius. It gives attachment, externally, to the Supinator brevis; 

 internally, to the Flexor longus pollicis, and between these to the Flexor digito- 

 rum sublimis. The middle third of the anterior border is indistinct and rounded. 

 Its lower fourth is sharp, prominent, affords attachment to the Pronator quadra- 

 tus, and terminates in a small tubercle, into which is inserted the tendon of the 

 Supinator longus. 



The posterior border commences above, at the back part of the neck of the 

 radius, and terminates below, at the posterior part of the base of the styloid pro- 

 cess ; it separates the posterior from the external surface. It is indistinct above 

 and below, but well marked in the middle third of the bone. 



The internal or interosseous border commences above, at the back part of the 

 tuberosity, where it is rounded and indistinct, becomes sharp and prominent as it 

 descends, and at its lower part bifurcates into two ridges, which descend to the 

 anterior and posterior margins of the sigmoid cavity. This border separates the 

 anterior from the posterior surface, and has the interosseous membrane attached 

 to it throughout the greater part of its extent. 



The anterior surface is narrow and concave for its upper two-thirds, and gives 

 attachment to the Flexor longus pollicis muscle ; below, it is broad and flat, and 

 gives attachment to the Pronator quadratus. At the junction of the upper and 

 middle thirds of this surface is the nutritious foramen, which is directed obliquely 

 upwards. 



The posterior surface is rounded, convex, and smooth in the upper third of its 

 extent, and covered by the Supinator brevis muscle. Its middle third is broad, 

 slightly concave, and gives attachment to the Extensor ossis metacarpi pollicis 

 above, the Extensor primi internodii pollicis below. Its lower third is broad, 

 convex, and covered by the tendons of the muscles which subsequently run in 

 the grooves on the lower end of the bone. 



The external surface is rounded and convex throughout its entire extent. Its 

 upper third gives attachment to the Supinator brevis muscle. About its centre 

 is seen a rough ridge, for the insertion of the Pronator radii teres muscle. Its 

 lower part is narrow, and covered by the tendons of the Extensor ossis metacarpi 

 pollicis and Extensor primi internodii pollicis muscles. 



The Lower extremity of the radius is large, of quadrilateral form, and provided 

 with two articular surfaces, one at the extremity for articulation with the carpus, 

 and one at the inner side of the bone for articulation with the ulna. The carpal 

 articular surface is of triangular form, concave, smooth, and divided by a slight 

 antero-posterior ridge into two parts. Of these, the external is large, of a trian- 

 gular form, and articulates with the scaphoid bone; the inner, smaller and 

 quadrilateral, articulates with the semilunar. The articular surface for the ulna 

 is called the sigmoid cavity of the radius ; it is narrow, concave, smooth, and 

 articulates with the head of the ulna. The circumference of this end of the bone 

 presents three surfaces, an anterior, external, and posterior. 



The anterior surface, rough and irregular, affords attachment to the anterior 

 ligament of the wrist-joint. The external surface is prolonged obliquely down- 

 wards into 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 outer surface of this process is marked 

 by two grooves, which run obliquely downwards and forwards, and are separated 



