OSTEOLOGY. 79 



and backwards. It is divided into an anterior and a 

 posterior part by a break in tlie margin. The anterior 

 part is continued on to tke posterior surface in forming the 

 small anterior articulatory facet for the inner small meta- 

 carpal bone. The posterior part is continuous with a small 

 facet for os trapezoides which, in its turn, joins an ex- 

 tremely small one for os metacarpi parvum internum. The 

 posterior margin is perfectly straight and about half the 

 size of the anterior. The outer margin anteriorly and 

 posteriorly is continuous with circulatory facets sloping 

 outwards, separated by a deep roughened dejDression, 

 These articulate with os unciforme, and are each con- 

 tinuous with an articulatory facet on the posterior surface 

 for the external small metacarpal bone. The iiiferior arti- 

 culatory surface is convex in every direction, and consists 

 of three prominences running from behind forwards. The 

 central prominence is most marked, narrowest, and extends 

 farthest both anteriorly and posteriorly. It is wholly 

 articulatory. The inner and outer prominences consist 

 of surfaces sloping towards the central ridge. They are 

 coated with cartilage continuous with that of the central 

 ridge. In most cases the inner is larger than the outer 

 articulatory surfaces. 



OSS A METACARPI' PARVA are extremely elongated 

 small bones, placed at the lateral, inclined to the posterior, 

 part of the large metacarpal bone. They decrease in size 

 from above downwards, terminating iv/eriorly oj^posite the 

 inferior part of the middle third of the large bone in small 

 rounded bulbs, from which the superior ligament of the 

 pad, and a small ligament to the infero-lateral part of the 

 large bone, run downwards. The siq^erior extremity is rough 

 and tuberous for the most part, while superiorly it is more 

 or less occupied by ai'ticulatory surfaces, which extend 

 slightly on to the attached part as two synovial facets 

 for OS metacarpi magnum. Below this the whole attached 

 surface is roughened for the white fibrous connection with 

 the large bone. The inner and otder surfaces are smooth, 

 and from the inner runs the anterior lumbricus muscle, 

 while the outer, with the large bone, forms a smooth 

 groove. 



The inner small metacarjKil hone at its upper extremity is 

 for the most part flat for articulation with os trapezoides. 

 Its outer margin anteriorly presents an almost vertical 



