RADIUS. 217 



Attachment of Muscles. To the olecranon : the Triceps, Anconeus, and one 

 head of the Flexor Carpi Ulnaris. To the coronoid process : the Brachialis 

 Anticus, Pronator Eadii Teres, Flexor Sublimis Digitorum, and Flexor Pro- 

 fundus Digitorum, occasionally, also the Flexor Longus Pollicis. To the shaft: 

 the Flexor Profundus Digitorum, Pronator Quadratus, Flexor Carpi Ulnaris, 

 Extensor Carpi Ulnaris, Anconeus, Supinator Brevis, Extensor Ossis Meta- 

 carpi Pollicis, Extensor Secundi Internodii Pollicis, and Extensor Indicis. 



THE EADIUS. 



The Eadius is situated on the outer side of the forearm, lying parallel with 

 the ulna, which exceeds it in length and size. Its upper end is small, and forms 

 only a small part of the elbow-joint ; but its lower end is large, and forms 

 the chief part of the wrist. It is one of the long bones, prismatic in form, 

 slightly curved longitudinally, and like other long bones has a shaft and two 

 extremities. 



The Upper Extremity presents a head, neck, and tuberosity. The head is of 

 a cylindrical form, depressed on its upper surface into a shallow cup, which 

 articulates with the radial or lesser head of the humerus in flexion of the joint. 

 Around the circumference of the head is a smooth articular surface, coated with 

 cartilage in the recent state, broad internally where it rotates within the lesser 

 sigmoid cavity of the ulna ; narrow in the rest of its circumference, to play in 

 the orbicular ligament. The head is supported on a round, smooth, and con- 

 stricted portion of bone, called the neck, which presents, behind, a slight ridge, 

 for the attachment of part of the Supinator Brevis. Beneath the neck, at the 

 inner and front aspect of the bone, is a rough eminence, the tuberosity. Its 

 surface is divided into two parts by a vertical line a posterior rough portion, 

 for the 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, sepa- 

 rated 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 Digitorum Sublimis. The middle third of the anterior border is indis- 

 tinct and rounded. Its lower fourth is sharp, prominent, affords attachment to 

 the Pronator Quadratus, 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 

 process ; 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 thejunction of the upper 

 and middle thirds of this surface is the nutrient foramen, which is directed 

 obliquely upwards. 



