128 THE SKELETON 



for the tendon*^ of the exicmor ossis metacarpi and extensor primi internodii pollicis. 

 The po.^terior surface is convex, and marked by three prominent ridges separatmg 

 three furrows. The posterior annular ligament is attached to these ridges, to 

 the '^tvloid process, and to the inner margin, thus forming with the bone a series 

 of tunnels. The outermost is broad, shallow, and frequently subdivided by a low 

 ridge The outer subdivision is for the extensor carpi radiahs longtor, the inner 

 for tiie extensor carpi radialis brevier. The middle groove is narrow and deep for 

 the tendon of the extensor secundi internodii pollicis. The innermost is shallow and 

 transmits the exten.^or indicis and the extensor communis digitorum which overlies 

 the indicis, the posterior branch of the anterior interosseous artery and the pos- 

 terior interosseous nerve, ^\'hen the radius and ulna are articulated, an additional 

 groove is formed for the extensor minimi digiti. 



Muscles. — The following muscles are attached to the radius: — 



Biceps. Pronator quadratus. 



Supinator brevis. Extensor ossis metacarpi pollicis. 



Supinator longus. Extensor primi internodii pollicis. 



Pronator radii teres. Flexor longus polHcis. 



Flexor sublimis digitorum. 



Ligaments: — 



Oblique ligament. Posterior annular. 



Interosseous membrane. External lateral of wrist. 



Anterior radio-ulnar. Interarticular fibro-cartilage of wrist. 



Posterior radio-ulnar. Anterior radio-carpal. 



Posterior radio-carpal. 



Blood-supply. — The nutrient artery is derived from the anterior interosseous 

 trunk ; it enters the shaft near the middle of the anterior surface, and runs towards 

 the proximal end of the bone. The head of the bone is supplied by the radial 

 recurrent and interosseous recurrent arteries. The low^er end is supplied by the 

 anterior and posterior interosseous arteries and numerous twigs from the carpal 

 arches. 



Ossification. — The radius is ossified by one primary and two secondary centres. 

 The shaft begins to ossify at the eighth week of embryonic life. The nucleus for 

 the lower end appears in the second year, whilst that for the upper end is deposited 

 in the fifth year. The head ankyloses with the shaft at the seventeenth year, but 

 consolidation is delayed at the lower end until the twentieth year. 



THE RAND 



The skeleton of the bund consists of three parts — the carpus, metacarpus, and 

 phalanges. 



TIIE CARPUS 



The carpus contains eight bones, arranged in two rows, four bones in each row. 

 Enumcnitcd from the radial to tlie ulnar side, the bones of the proximal row are, 

 the scaphoid, semilunar, cuneiform, and pisiform ; those of the distal row, the 

 trapezium, trapezoid, magnum, ;in(l unciform. The anterior and posterior 

 surfaces of all the (•ar])al l)ones, except the i)isiform and cuneiform, are non-artic- 

 ular; the anterior surfaces of the bones of the upper row are larger than the pos- 

 terior, but in the lower row this arrangement is reversed. 



