1P.4 



THE SKELETON 



articular surfaeo for the base of the first phalanx, and is more extensive on the 

 ])almar than the dorsal aspect. On its palmar surface the head is grooved for flexor 

 tendons, each comer of the groove being surmounted by a tubercle. The sides of 

 th." head are com])ressed, and each side is occupied by a well-marked fossa. 



The several metacarpals present distinctive characters. The First is the most 



Fig. 144.— The Fikst (Left) Metacakpal, 



RADIAL SIDE 



ULNAR SIDE 



])eculiar; it is the shortest, and its shaft resembles that of a phalanx. It has a 

 concave palmar surface, and the dorsal surface lacks the bifurcated ridge. The 

 base has a saddle-shaped articular surface for the trapezium, and at its outer 

 (radial) comer presents a tubercle for the insertion of the extensor ossis metacarpi 

 pollic'is. The head of the bone presents on its palmar aspect two shallow grooves 

 for the sesamoids in the ^exor brevis pollicis. 



Fig. 145. — The Second (Left) Metacakpal. 



RADIAL SIDE 



(OR TRAPEZIUM 



ULNAR SIDE 



Muscles : — 



FOR THIRD METACARPAL 

 FOR MAGNUM 



Extensor ossis metacarpi pollicis. 

 Opj)oncns pollicis. 



Fir;-t dorsal interosseous. 

 Interosseus primus volaris. 



Blood-supply.— The nutrient vessel is derived from the ])rinceps pollicis arterv 

 it entir> uu the ulnar side, and is directed towards the head of the bone. 



