OF COLYMBUS TORQUATUS 153 



Upon the superior surface of the bone there runs longitudinally the continuation of the 

 deep groove of the radius which lodges the extensor metacarpi radialis. At right angles 

 with this and running transversely, there is a still deeper groove which conducts the ten- 

 don of the flexor metacarpi radialis. 



The second, smaller bone of the carpus, which represents the second row of carpal bones, 

 is placed just in the bend of the joint, on the ulnar side, wedged in between the ulna and 

 metacarpus, with both of which it articulates. Its ulnar aspect presents a smooth, oval, 

 somewhat depressed facet, which plays against the extremity of the large articulating 

 surface of the ulna. Its metacarpal aspect presents a very deep horizontal notch or fis- 

 sure, into which is received the inferior thin border of the metacarpal bone. In flexion 

 and extension of the metacarpus, this small bone rides backwards and forwards along the 

 edge of the metacarpal bone, being as it were astride of the latter. The non-articular 

 aspects of the bone are rough for the attachment of tendons. 



Metacarpus. In the single metacarpal bone, which, as in all birds, results from the fusion 

 of the five of the human species, there may be clearly traced three distinct bones. 



The first, which corresponds to the metacarpal of the thumb, is found superimposed upon 

 the radial edge of the metacarpus, and intimately blended with it, appearing like an elevated 

 crest. It is about one and a half inches long, and bears upon its distal extremity the pollex 

 or thumb. 



The second, or metacarpal of the little finger, lies directly upon the ulnar side of the bone, 

 and is much more distinct than the preceding. It is from its origin for about half an inch, 

 fused with the main bone, but then becomes entirely separated from the latter by a 

 considerable hiatus, running forward to be again united to it about half an inch from its 

 distal extremity. It supports upon its tip the "ulnar finger." 



The remaining greater portion of the metacarpus results from the coalescence of the 

 three middle bones of the human hand. This supports the three phalanges of the "radial 

 finger," and articulates with the radius and ulna. 



The metacarpus, thus constituted, is a strong bone, nearly four inches long by about five 

 eighths of an inch broad at the broadest part, much compressed. Its proximal extremity is 

 taken up wholly by a single large, smooth, articulating facet, which moves upon the ulna 

 and both of the carpal bones, but has no connection with the radius, the large carpal bone 

 being interposed between it and the head of the latter. This articulating surface is 

 exceedingly convex from the radial to the ulnar side ; but presents in the median line 

 a deep sulcus running its whole length, causing the transverse outline of the head to be 

 concave. The greater part of the head is joined by a strictly ginglymoid articulation to 

 the central portion of the large facet on the ulna. At the radial side the articulation is 

 with the large carpal bone ; at the ulnar, the inferior border is prolonged backwards, and 

 forms the prominent ridge over which rides the smaller carpal bone, as already described. 

 On either side of the articulating surface the bone presents rough elevations and depres- 

 sions for the insertion of tendons and ligaments. On its superior aspect the bone is also 

 marked with several longitudinal grooves, which lodge the tendons that are inserted into 

 the phalanges. 



Phalanges. The pollex, or thumb, is a short, perfectly straight bone, which projects one 

 inch beyond the abrupt termination of the crest-like elevation corresponding to the first 

 metacarpal bone. It is much compressed laterally, and terminates in a truncated sharp 

 edge. It is movably articulated with the metacarpal bone, but really has but very slight 

 motion. 



