MECiALONYX. 31 



The specimen of a lunar bone in the Dickeson collection besides being smaller, 

 is relatively narrower transversely, and its distal articulation forms a plane instead 

 of being concave, and inclines towards the radial side, except at the forepart, where 

 it is partially bent to the opposite side. 



Os Caneiforme. — (PI. VIII, Figs. 9, 11, B.) The cuneiform bone is irregularly 

 pyramidal, and second in size in the carpus. 



The specimen is broken at its dorsal surface, but this appears to have been as 

 extensive as the palmar surface, which is large, irregular, and perforated. (Fig. 

 9, B.) 



The proximal surface of the bone exhibits a broad transverse convexity (Fig. 9, 

 B, e ; Fig. 11, B, c), for articulation with the ulna, narrowing antero-posteriorly 

 towards the inner extremity, which is bent forward to articulate with the pisiforme. 

 (Fig. 9,/; 11, (Z.) 



The distal surface presents a broad, transverse, sigmoid concavity for conjunction 

 with the unciforme, and at its inner extremity is bent backwards to join the meta- 

 carpal of the little finger. 



Os Pisiforme. — (PI. VIII, Fig. 14.) The pisiforme is an irregular, oblong, lenti- 

 cular bone, with an obtuse margin. Its dorsal surface is a little convex and rough 

 for tendinous attachment. The palmar surface is concave superiorly ; and forms a 

 prominent ovoidal tuberosity below. The antero-external margin presents a single, 

 elliptical, articular surface (Fig. 14, a), bent near its middle ; the lower portion 

 being intended to join the cuneiforme, the other portion to join the ulna. The 

 specimen in the collection of Dr. Dickeson, is a fifth smaller than that described, 

 and it has its articular surface more bent at the middle. 



Os Magnum. — (PL VIII, Figs. 10, 12, 13, A.) The os magnum, in this instance 

 indicating the impropriety of many names in anatomy, is the smallest bone of the 

 carpus. It is irregularly wedge-shaped, and is situated between the scapho-trapezial, 

 lunar, trapezoid, unciform, and median metacarpal bones, with all of which it arti- 

 culates. Proximally it presents an oblique plane (Figs. 10, 12, cl), for articulation 

 with the lunar bone ; and continuous with this facet on the inner side is one for 

 the unciform bone. 



On the outer side it presents at the dorsal border a tripartite articular facet, 

 separated by a deep interarticular groove from an oval facet at the palmar border. 

 The tripartite facet articulates with the scapho-trapezial, the trapezoid, and median 

 metacarpal bones; and the oval facet (Figs. 10, 12, c) articulates with the trapezial 

 portion of the scapho-trapezium. 



The distal surface presents two articular facets ; an inner one (Fig. 13, d), extend- 

 ing from the dorsal to the palmar borders, and an outer one (Fig. 13, c), constitut- 

 ing a portion of the tripartite f\icet above mentioned, and separated from the other 

 by an interarticular tract. The two distal articular facets join the median meta- 

 carpal bone, but the corresponding surface on a specimen of the latter (PI. X, Fig. 

 13), belonging to a diflerent skeleton, is undivided, that is to say, there is no inter- 

 articular tract separating the smaller from the larger articular facet. 



The dorsal and palmar surfaces, of which the latter (PI. VIII, Fig. 10) ia the 

 larger, are irregular and perforated for ligamentous attachment. 



