THE BONES OF THE UPPER LIMB 203 



lunar. The internal surface, which represents the rounded apex, 

 is of hmited extent, and rough for the internal lateral ligament of 

 the wrist- joint. The palmar surface presents a circular, slightly 

 convex facet, which occupies rather more than the inner and 

 lower half, and articulates with the pisiform, the rest of the surface 

 being rough. The supero-posterior surface is divisible into two parts, 

 outer and inner. The outer portion, which is close to the base, 

 presents a convex facet for the inferior surface of the triangular 

 interarticular libro-cartilage. The inner portion is marked by two 

 rough oblique grooves, superior and posterior, separated by a ridge 

 which is dorsally placed. The inferior surface presents a large 

 triangular facet, concavo-convex from without inwards, for the 

 unciform. 



Articulations. — Superiorly with the triangular interarticular 

 libro-cartilage, inferiorly with the unciform, externally with the semi- 

 lunar, and anteriorly with the pisiform. 



The Pisiform Bone. 



The pisiform bone is characterized by its resemblance to a pea, 

 and is placed in front of the cuneiform, which constitutes its only 

 articulation. It is irregularly round, except posteriorly, where it 

 presents over its upper three-fourths a circular, slightly concave 

 facet for the cuneiform, the lower fourth being non-articular. The 



Superior Aspect 



Ulnar Groove 



(on External Surface) 



For Cuneiform 



(on Posterior Surface) 



Fig. 116. — The Right Pisiform Bone (Postero-external View). 



long axis of the bone is directed downwards and slightly outwards. 



The palmar surface gives attachment superiorly to the flexor carpi 

 ulnaris, inferiorly to the pisi-uncinate and pisi-metacarpal ligaments, 

 and abductor minimi digiti, and extemall}' to a portion of the 

 anterior annular ligament. The internal surface is irregularly 

 convex, and the external presents the ulnar groove, which lodges 

 the ulnar nerve and artery. 



The Trapezium. 



The trapezium is the external bone of the second row, and is 

 characterized by a groove and ridge on its palmar surface, and a 

 saddle-shaped facet on its inferior surface. It is polyhedral, 



