164 



EXTREMITY. 



tious foramen, the canal following the same 

 direction as that of the ulna, namely upwards. 

 The muscles attached to the anterior surface of 

 the radius are the flexor pollicis proprius, con- 

 nected with the two superior thirds of the bone, 

 and the pronator quadratus occupying the 'in- 

 ferior third. The posterior surface of the radius 

 is likewise inclined, and looks backwards and 

 inwards, very narrow in its whole extent, but 

 broadest at its inferior extremity, convex in its 

 superior and inferior thirds, and slightly con- 

 cave from above downwards in its middle third. 

 This last portion of the bone affords attachment 

 to the two inferior extensor muscles of the 

 thumb ; the superior third is embraced by the 

 supinator brevis, and the inferior third has 

 applied to it the tendon of the common extensor 

 of the fingers, the indicator, and the extensor 

 tertii internodii pollicis. The external surface 

 is convex in its whole extent, and like the 

 others expands inferiorly; about its middle we 

 observe a rough surface, which gives insertion 

 to the pronator quadratus ; in its upper portion 

 the surface is embraced by the supinator brevis, 

 and inferiorly the radial extensors of the wrist 

 are applied to it. 



Of the three edges which separate these sur- 

 faces, the internal is sharp, and extends from 

 about an inch below the bicipital tuberosity to 

 about the same distance above the carpal extre- 

 mity of the radius; at this latter point the edge 

 seems to bifurcate and form a plane triangular 

 surface above the inferior extremity of the ra- 

 dius. This edge gives attachment in its entire 

 extent to the interosseous ligament. The an- 

 terior edge is rounded ; it distinctly originates 

 from the bicipital tuberosity, and terminates at 

 the outer side of the carpal extremity of the 

 radius in front of the styloid process. 'The su- 

 pinator brevis, the proper flexor of the thumb, 

 and the flexor sublimis of the fingers, have 

 attachments to this edge above, and below 

 the pronator quadratus and supinator longus 

 are inserted into it. The posterior edge is very 

 imperfectly defined, being distinct only in its 

 middle. 



The inferior or carpal extremity of the radius 

 is the largest part of the bone ; it is irregularly 

 quadrilateral in form. Its inferior surface 

 forms an articular excavation, the outline of 

 which is triangular, the apex being external 

 and the base internal ; this surface is divided 

 into two by a slightly prominent line which 

 passes from before backwards ; the outer of 

 these two portions retains the triangular form, 

 and is articulated with the scaphoid bone of 

 the carpus; the internal is quadrilateral, and 

 articulated with the lunar bone. At its inner 

 margin, this surface is continuous with a slightly 

 excavated articular facet on the ulnar side of 

 the inferior extremity of the bone, which is 

 articulated with the convex surface on the cor- 

 responding part of the ulna. The inferior ex- 

 tremity of the radius presents, at its outer part, 

 a pyramidal process projecting downwards and 

 slightly outwards ; this is the styloid process, 

 which by its apex gives attachment to the ex- 

 ternal lateral ligament of the wrist-joint. The 

 anterior margin of the inferior extremity is 



slightly concave from side to side ; it gives at- 

 tachment to the anterior ligament of the wrist- 

 joint, and the tendons of the flexor muscles of 

 the fingers pass over it into the palm of the hand. 

 On the posterior margin of this extremity we 

 observe two grooves : the internal one, wide and 

 very superficial, lodges the tendons of the com- 

 mon extensor of the fingers and the indicator ; 

 the exteraal, deeper and oblique, lodges the 

 extensor tertii internodii pollicis. Externally 

 we notice likewise two superficial grooves, of 

 which the posterior lodges the radial extensors 

 of the wrist, and the anterior is traversed by the 

 extensores primi et secundi internodii pollicis. 



Structure. The central canal extends up- 

 wards into the neck of the bone; it is cylin- 

 drical at the extremities, and prismatic in the 

 centre. Both extremities are composed of can- 

 cellated structure. 



Developement of' the bones of the fore-arm. 

 Both bones appear about the same time, and if 

 not synchronously with the humerus, at least a 

 very little later. With both bones the ossifi- 

 cation begins on the shafts, which are very 

 early completed ; the ossific point of the shaft 

 of the radius is said, by Beclard and Cruveil- 

 hier, to begin some days before that of the 

 ulna. In the radius the inferior extremity 

 begins to ossify before the superior, about the 

 end of the second year. The ossification of 

 the superior extremity begins between the 

 seventh and ninth year; it is united to the 

 shaft about the twelfth year, whilst the inferior 

 extremity, whose ossification begins earlier, is 

 not united till the eighteenth or twentieth year. 

 The progress of the ossification of the ulna is 

 very similar. The inferior extremity developed 

 by a single point of ossification begins first, 

 about the sixth year. A little later the olecra- 

 non begins to ossify; the coronoid is formed 

 by an extension of ossification from the 

 shaft. The union of the superior extremity of 

 the ulna with the shaft takes place about the 

 fifteenth or sixteenth year ; that of the inferior 

 about the eighteenth or twentieth. 



It is important to observe that the articula- 

 tion of the radius with the ulna, in the manner 

 in which it is effected in man, has reference to 

 the motions of the hand. Pronation and supi- 

 nation of the hand are effected by the rotation 

 of the head of the radius within the coronary 

 ligament and on the lesser sigmoid cavity of 

 the ulna. The hand is so connected with the 

 radius that it follows the motions of that bone; 

 when, therefore, the radius rotates in such a 

 direction that its inferior part crosses the ulna, 

 the posterior edge is directed outwards, and its 

 anterior surface inwards and backwards; the 

 palm of the hand is turned backwards and the 

 dorsum forwards; the forearm and hand are 

 then said to be in pronation. On the contrary, 

 when the rotation is such that the ulna and ra- 

 dius are placed on the same plane, the dorsum 

 of the hand is directed backwards and the palm 

 forwards ; this is supination. 



In the lower animals we never find this mode 

 of articulation of the radius with the ulna, 

 unless there be also present the motions of su- 

 pination and pronation of the hand. In such 



