THOEACIC LIMBS 609 



facet on the under surface of the scapho-lunar. The proximal surface 

 on the radial side of this facet is rough and convex ; it turns down 

 into the radio-dorsal and dorsal surfaces. 



The inner larger portion of the proximal surface is converted into 

 a deeply concave crescentic articular surface, which runs forward and 

 inward and slopes down in front to meet the distal surface, forming, as 

 already explained, the sharp dorso-ulnar border. This facet is sepa- 

 rated behind from the palmo-ulnar surface by an elevated crest. It 

 also articulates with the facet on the distal surface of the scapho-lunar. 



The radio-dorsal surface is slightly convex from before backward. 

 It is longer than high ; in outline triangular, the apex of the triangle 

 at the radio-palmar angle and the base passing by a convexity into 

 the dorsal surface. It is slightly roughened, and gives attachment to 



ligaments. 



FIG. 472. 

 Palmar Side. 



&^\ 



With Tmpezium.~J^I^\ With Ma ffnum. 



Radial Side. ; ^jSL ' Ulnar Side. 



* With Scapho-lunar. 



Dorsal Side. 



LEFT TRAPEZOID, PROXIMAL SURFACE. 



The dorsal surface is also triangular ; the base of the triangle is 

 applied to the base of the triangular radio-dorsal surface, and the apex 

 reaches the outer end of the dorso-ulnar border. It is convex from 

 side to side, and slopes upward and backward to pass into the dorsal 

 end of the proximal surface. 



The palmo-ulnar surface is twice as long as high. Its palmar 

 border is straight, its proximal and distal borders slightly arcuate, 

 meeting in front at quite an acute angle. It is almost flat, and rough, 

 and is bound by strong ligaments to the rough surface on the outer 

 side of the magnum. 



The dorso-ulnar border is about half as long as the palmo-ulnar 

 surface. It is faintly emarginate, and limits the deep articular con- 

 cavity on the proximal surface. 



The radio-palmar surface is also twice as long as high, and is 

 nearly flat, except at its radio-distal angle, which slopes downward and 

 forward into the distal surface. Its ulnar border is straight, and runs 



