204 



A MANUAL OF ANATOMY 



and its long axis is directed downwards and inwards. The 

 superior surface presents a semi-oval, concave facet for the 

 scaphoid. The inferior surface presents a saddle-shaped facet, 

 concave from side to side, convex from before backwards, and 

 directed outwards as well as downwards, for the base of the first 

 metacarpal bone. The internal surface has two facets — an upper, 

 which is large and concave, for the trapezoid, and a lower, which is 

 small, for the base of the second metacarpal bone. The external 

 surface is broad, pentagonal, and rough. The palmar surface, 

 rough and elongated from above downwards and inwards, is broad 

 above and narrow below. Superiorly it presents a deep groove, 

 directed downwards and inwards, which transmits the tendon of 

 the flexor carpi radialis, and external to this groove a prominent 

 ridge, called the tuberosity, which gives attachment to the anterior 

 annular ligament, abductor pollicis, and opponens pollicis. The 



Tuberosity 



Groove for Flexor 

 Carpi Radialis 



Inferior Surface 

 for 1st Metacarpal. 



^ For Scaphoid 

 (on Superior Surface) 



"For Trapezoid 



(on Internal Surface) 



For 2nd Metacarpal 

 For 2nd Metacarpal (on internal Surface) 



Fig. 117. — The Right Trapezium. 

 A, Antero-inferior View ; B, Supero-internal View. 



dorsal surface is broader than the palmar, and its inferior and 

 internal angle is much elongated towards the base of the second 

 metacarpal bone, with which it articulates by the small facet on 

 its inner aspect. 



Articulations. — Superiorly with the scaphoid, inferiorly with the 

 first metacarpal, and internally chiefly with the trapezoid, but also 

 with the second metacarpal. 



The Trapezoid Bone. 



The trapezoid bone somewhat resembles the trapezium, but it is 

 destitute of a groove and tuberositv. Its antero-posterior diameter 

 is longer than the transverse. The palmar surface is small and 

 pentagonal, and it gives origin to fibres oi the adductor obliquus 

 pollicis. The dorsal surface is large and has its internal and inferior 

 angle elongated towards the styloid process of the third meta- 



