198 SPECIAL ANATOMY OF THE SKELETON 



rough, for the attachment of ligaments. The anterior or palmar surface presents, 

 at its inner side, an oval facet, for articulation with the pisiform, and is rough 

 externally, for ligamentous attachment. The external surface, the base of the 

 pyramid, is marked by a flat, quadrilateral, smooth facet, for articulation with 

 the semilunar. The internal surface, the summit of the pyramid, is pointed and 

 roughened, for the attachment of the internal lateral ligament of the wrist. 



To ascertain to which hand this bone belongs, hold it so that the base is directed backward, 

 and the articular facet for the pisiform bone upward; the concave articular facet will point to 

 the side to which the bone belongs. 



Articulations. With three bones the semilunar externally, the pisiform in front, the unci- 

 form below; and with the triangular, interarticular fibrocartilage which separates it from the 

 lower end of the ulna. 



The pisiform (os pisiforme) (Fig. 156) may be known by its small size and by 



its presenting a single articular facet. It is situated on a plane anterior to the 



other bones of the carpus; it is spheroidal in form, with its long 



For cuneiform ,. j. , ,, 



J j diameter directed vertically. 



Surfaces. Its posterior surface is a smooth, oval facet, for 

 articulation with the cuneiform. This facet approaches the 

 superior, but not the inferior border of the bone. The anterior 

 FIG. 156. The left O r palmar surface is rounded and rough, and gives attachment to 



pisiform, showing, . . , .,. 



posterior and lateral the anterior annular ligament and to the Plexor carpi ulnans 

 and origin to the Abductor minimi digiti. The outer and inner 

 surfaces are also rough, the former being concave, the latter usually convex. 



To ascertain to which hand this bone belongs, hold the bone with its posterior or articular 

 facet downward and the nonarticular portion of the same surface backward; the inner concave 

 surface will point to the side to which it belongs. 



Articulations. With one bone, the cuneiform. 



Attachment of Muscles. To two the Flexor carpi ulnaris and Abductor minimi digiti; 

 and to the anterior annular ligament. 



Bones of the Lower Row. The trapezium (os multangulum majus) (Fig. 

 157) is of very irregular form. It may be distinguished by a deep groove, for 

 the tendon of the Flexor carpi radialis muscle. It is situated at the external and 

 inferior part of the carpus between the scaphoid and first metacarpal bone. 



Groove For sca P J ' oid 



Fortrapezoid _^, jfj*^ For trapezoid 



W-''-^$&>^ 

 -Ridge 



For 2nd 

 metacarpal 



For 1st metacarpal for 2nd metacarpal 



A B 



FIG. 157. The left trapezium. A, as seen from in front; B, from above and mesal side. 



Surfaces. The superior surface, concave and smooth, is directed upward and 

 inward, and articulates with the scaphoid. The inferior surface, directed down- 

 ward and inward, is oval, concave from side to side, convex from before backward, 

 so as to form a saddle-shaped surface, for articulation with the base of the first 

 metacarpal bone. The anterior or palmar surface is narrow and rough. At its 

 upper part is a deep groove running from above obliquely downward and inward; 

 it transmits the tendon of the Flexor carpi radialis, and is bounded externally 



