224 



OSTEOLOGY. 



Head 



Shaft 



Head 



Tubercle 



head. The surface included between the two lines is smooth and of elongated 

 triangular form. On either side of these lines two broad shallow grooves wind 

 spirally on to the volar surface, where they are separated 

 by a sharp ridge which is continuous with a somewhat 

 triangular surface which corresponds to the volar aspect 

 of the base. The grooved surfaces on either side of the 

 shaft furnish origins for the interossei muscles. Close to 

 the volar crest is the opening of the nutrient canal, which 

 is directed towards the proximal extremity, except in the case 

 of the first metacarpal bone. 



The capitulum (head) is provided with a surface for 

 articulation with the proximal phalanx. This area curves 

 farther over its volar than its dorsal aspect. Convex from 

 before backwards and from side to side, it is wider anteriorly 

 than posteriorly ; notched on its volar aspect, its edges form 

 two prominent tubercles, which are sometimes grooved for 

 the small sesamoid bones which may occasionally be found 

 on the volar surface of the joint. On either side of the head 

 of the bone there is a deep pit, behind which is a prominent 

 tubercle ; to these are attached the collateral ligaments of the 

 metacarpo-phalangeal joints. 



The bases, 

 all more or less 



wedge-shaped in 



Fia. 222. FIRST RIGHT r f . , , 



METACARPAL BONE. form, articulate 

 with the carpus; 



they differ in size and shape according 

 to their articulation. 



Of the five metacarpal bones, the 

 first, viz., that of the thumb, is the 

 shortest and stoutest, the second is the 

 longest, whilst the third, 

 fourth, and fifth display a 

 gradual reduction in length. 



The medial four bones 

 articulate by their bases 

 with each other, and are 

 united at their distal ex- 

 tremities by ligaments. 

 They are so arranged as to 

 conform to the hollow of 

 the palm, being concave 

 from side to side anteriorly, 

 and convex posteriorly. The 

 first metacarpal differs from 

 the others in being free at capitate bone 

 its distal extremity, whilst 

 its proximal end possesses 

 only a carpal articular facet. 



The first metacarpal 



bOne iS the Shortest and Lesser multangular 



Stoutest of the series. Its FIG. 223. SECOND RIGHT METACARPAL BONE. 



body 18 compressed from NOTE. The bone is represented in the centre of the figure in the 



haoVwarrU Ttfi head position which it occupies in the right hand viewed from the volar 



Lesser 

 multangular 



Greater 

 multangular 



v vl spect. The views on either side, and below, represent respectively 



01 large Size, IS but Slightly tne corresponding surfaces of the bone turned towards the reader. 



convex from side to side, and 



is grooved on its volar aspect for the sesamoid bones. The base is provided with 

 a saddle-shaped surface for articulation with the greater multangular, and has no 

 facets on its sides. Laterally there is a slight tubercle to which the abductor pollicis 



