OSTEOLOGY. 



75 



sligMly rougli for attacliment of the annular ligament. 

 At'^its antero-superior part it presents a small articulatory 

 facet continuous with the superior facet on the anterior 

 margin. From this a ridge runs downwards and backwards 

 obliquely to the inferior margin. 



- OS TRAPEZOIDES is the inner bone of the lower row, 

 and articulates with magnum, scaphoides, metacarpi mag- 

 num, and parvum internum (sometimes with pisiform). 

 It presents three surfaces. The supero-iuternal surf ace pre- 

 sents superiorly a rounded convexity, which commencing 

 in a point at the outer margin anteriorly occupies the whole 

 upper part of the bone, and passes to the postero-internal 

 part, extending about halfway down to the lower surface. 

 Around it runs a narrow groove, exce^Dt at the outer part, 

 where it is continuous with a small elongated facet, articu- 

 latory for OS magnum. The rest of this surface is roughened 

 for attachment of the annular, inner lateral, and connecting 

 ligaments. Along the inferior margin is a groove which 

 bounds the inferior articulatory surface. The inferior surface 

 is mainly occupied by a flat facet for articulation with the 

 inner small metacarpal bone, elongated from before back- 

 wards, posteriorly continuous with a smaller facet for os 

 metacarpi magnum, and this in turn is continuous with a 

 still smaller facet for os magnum. This articulatory sur- 

 face is bounded on every side by a groove, except on the 

 outer, where it is reflected on to the outer surface for arti- 

 culation with OS magnum. Between the superior facet 

 (continuous with the upper surface) and the inferior facet 

 (continuous with the lower surface) the outer part of the 

 bone is roughened for attachment of interosseous ligaments. 

 Postero-inferiorly is a peculiar prominence presenting a 

 sharp point inwards, bounded by the posterior surface for 

 OS magnum posteriorly, inferiorly by the facet for os meta- 

 carpi magnum. 



OS MAGNUM is the central bone of the lower row, and 

 articulates with lunare, scaphoides, trapezoides, unciforme, 

 metacarpi magnum, et parvum internum. It has five 

 surfaces, which give it a triangular appearance, and is flat- 

 tened from above downwards, having a base or anterior 

 surface, and an apex or posterior angle which is rounded. 

 The superior surface is triangular and presents two articu- 

 latory portions which blend anteriorly. The outer consists 

 of two triangular portions united at their apices, occu- 



