THE META CA RP US 



185 



The 8Eeoxi) Metacarpal is the longest, and is easily recognised by its large 

 deeply cleft base. 



The dorsal surface affords attachment to the tendon of the extensor carpi radialis 

 loiu/ior and a part of the extensor carpi radialis hrevior ; to the palmar surface the 

 tendon of the flexor carpi radialis is inserted. The remaining surfaces present four 

 articular facets. The end of the bone is occupied by a deep groove for the trape- 

 zoid; the ulnar ridge of this concavity is smooth for the magnum, and is directly 

 (•(»ntinuous with a long narrow facet for the third metacarpal. The radial surface 

 of the base has a small, somewhat quadrangular facet for the trapezium. 



Muscles : — 



Flexor ear{)i radialis. 

 Extensor earpi radialis longior. 

 Extensor carpi radialis brcvior. 



First and second dorsal interosseous. 

 First palmar interosseous. 

 Flexor brevis pollicis. 



Fig. 14G.— The Third (Left) Metacakpal. 



RADIAL SIDE 



FOR SECOND METACARPAL 



ULNAR SIDE 



FOR FOURTH METACARPAL 



STYLOID PROCESS 



Blood-supply. — The nutrient artery is derived from the first palmar inter- 

 osseous. It enters on the ulnar side, and is directed towards the proximal end or 

 base of the l)one. 



The Third Metacarpal is easily recognised by the prominent styloid process 

 Avhich projects from the radial corner of the dorsal surface of the base. A little 

 below this process the extensor carpi radialis brevior finds insertion. The carpal 

 .«urface of the base is nearly plane for the magnum. The radial surface has a long 

 narrow facet for the second metacarpal. On the ulnar side, two rounded facets are 

 usually seen for the fourth metacarpal. Not unfrequently one of them is absent. 



Muscles : — • 



Extensor carpi radialis brevior. 



Adductor ])ollicis. 



Second and third dorsal interosseous. 

 Flexor carpi radialis. 



Blood-supply. — The nutrient artery is derived from the interosseous: it enters, 

 as a rule, on the radial side, and is directed towards the base. 



The Fourth Metacarpal has a very small base. By its carpal surface it articu- 

 lates with the unciform. The radial surface has two rounded facets for the third 

 metacarpal; there is a small facet for the magnum at the posterior radial coiTier. 

 The ulnar side has a narrow articular surface for the fifth metacarpal. 



