Hatch i.R : Iokk I,imi! and Manus of ]5ront(,)Saurus. 3()9 



I. These bones are so interlocked that when placed in position a 

 considerable portion of the proximal end of mc. II. is covered over 

 by the superior border of the cavity in nic. [., while the j)ro\inial 



Fig. 12. \'ie\v of proximal extremities of metacarpals of rit^ht manus in position 

 about one-fourth natural size. (No, 563.) 



end of the latter is raised above that of mc. II. so as to articulate di- 

 rectly with the radius. There is a broad, shallow excavation on the 

 external lateral surface at the proximal end of mc. II. for the recep- 

 tion of the internal proximal angle of mc. III. The proximal artic- 

 ular surface of mc. II. is broad above and somewhat narrowed in- 

 feriorly. Its superior and inferior margins are bounded by nearly 

 straight, horizontal lines. The surface is very slightly and regularly 

 convex in all directions. The distal articular surface is broad and 

 deep, though in the present specimen the latter diameter has been 

 somewhat diminished by pressure. Just anterior to the rugosity on 

 the internal lateral surface of the [proximal end of this bone there is 

 a deep groove leading obliquely downward and forward to the palmar 

 surface. This may have served for the transmission of a flexor tendon. 

 Metacarpal III. is of equal length, but decidedly more slender than 

 mc. II. The superior surface is smooth and regularly convex. There 

 is a noticeable lateral constriction at about the middle of the distal 

 one-half of the bone. On the internal lateral surface of the proximal 

 end there is a flat rugo.se area, broad proximally, but narrowed dis- 

 tally, which disappears toward the middle of the shaft. The internal, 

 proximal, lateral angle is so shaped as to fit nicely into the cavity on 

 the external lateral surface of the proximal end of mc. II., causing an 

 interlocking of the proximal ends of these bones. The proximal ar- 

 ticular surface is subtriangular in outline through the external superior 



