THE BONES OF THE UPPER LIMB 213 



margin of the shaft gives insertion to the opponens minimi digiti, 

 and the shaft also affords origin to the fourth dorsal, and third 

 palmar, interossei. 



Articulations. — Superiorly with the unciform, externally with the 

 fourth metacarpal, and inferiorly with the first phalanx of the 

 little finger. 



Each metacarpal bone presents a medullary foramen, that of 

 the first, and usually that of the second, being situated on the 

 inner or ulnar side of each shaft, whilst those of the third, fourth, 

 and fifth are situated on the outer or radial side* The foramen of 

 the first and the canal to which it leads are directed downwards 

 towards the head, but those of the other four are directed upwards 

 towards the base. The medullary artery of the first metacarpal is 

 furnished by the arteria princeps pollicis, those of the second and 

 third are branches of the first palmar interosseous, that of the 

 fourth is furnished by the second palmar interosseous, and that of 

 the fifth by the third palmar interosseous, arteries. 



Structure. — ^The structure is that of a long bone. 



Tubetoaty 



k 



For 



ForOs Unciform 

 Magnum 



Fig. 126. — The Bases of the Right Metacarpal Bones (Superior View). 



The metacarpus as a whole is concave from side to side, and also 

 longitudinally, on its palmar aspect, whilst the dorsal aspect is con- 

 vex. The first metacarpal stands off at an angle from its fellows, 

 and occupies a more anterior plane, thus fitting it for the important 

 movement of opposition on the part of the thumb. The other fovur 

 metacarpals lie very nearly parallel with each other. They articu- 

 late with one another by their bases, but diverge slightly towards 

 their heads, where they are connected on their palmar aspects by 

 the transverse met icarpal ligament. Between the five bones there 

 are four intervals, called interosseous spaces, the first being that 

 between the first and second bones. 



The Phalanges. 



The phalanges are also known as ossa internodia, from their 

 position between the joints of the fingers. The fingers, of which 

 they form the framework, are called poUex or thumb, index, middle, 



* Of 100 second metacarpal bones examined, 59 had the medullary foramen 

 on the inner side, and 4 1 on the outer. 



