198 SKELETON. 



Of the First Metacarpal Bone, or that of the Thumb. It is 

 placed upon the trapezium: and besides being the shortest, is 

 also the thickest of any. Its upper end is cylindrical and 

 slightly concave from side to side, to present a fit surface to 

 the trapezium. Its lower end is slightly convex, and elongated 

 in front into a trochlea, on either side of which reposes a sesa- 

 moid bone. The posterior face of its body is flat and straight; 

 the anterior is concave in its length, and is divided into two 

 surfaces by a middle ridge. A roughness exists on either side, 

 at its lower end, for the attachment of the lateral ligament. 



Of the Second Metacarpal Bone, or that of the Fore Finger. 

 The greater length of this bone gives it a distinctive character. 

 It is placed upon the trapezoides, and articulates laterally also 

 with the trapezium, and the magnum. Its carpal or upper end 

 presents, in the middle, a deep concavity for receiving the tra- 

 pezoides, at the radial side of which is a small plane face for 

 articulating with the trapezium, and at the ulnar side an oblong 

 surface, the upper margin of which joins the magnum, and the 

 remainder is in contact with the third metacarpal bone. The 

 lower end presents a convex head extended in front to concur 

 in the flexion of the finger, on each side of which head is a 

 concave rough surface for the lateral ligament. The poste- 

 rior face of the bone presents a triangular flat surface, the base 

 of which is towards the finger or phalangial end. The palmar 

 face is concave, longitudinally, and divided by a middle ridge, 

 into two surfaces, each of which is compressed by the interos- 

 seous muscles. A tubercle exists on the back of the bone just 

 below its carpal end for the insertion of the tendon of the ex- 

 tensor carpi longior, and another in front for that of the flexor 

 radiali?. 



Of the Third Metacarpal Bone. This is a little shorter than 

 the last, and is nearly of the same size, but its carpal extremity 

 is very different. The latter is triangular, and is bounded on 

 its radial side by a sort of styloid process, with a tubercle on 

 the posterior face of it, into which the tendon of the extensor 

 radialis brevior is inserted. It is placed upon the magnum, to 

 which it joins by a slighlly concave, winding surface. It also 

 presents, continuous with the same surface, an oblong face 



