370 Annals of the Carnegie Museum. 



lateral angle of the proximal end being produced into a strong tri- 

 angular process which overlies a corresponding projection on the in- 

 ternal inferior lateral angle of mc. I\^. The external outer margin of 

 this process on mc. III. presents a rounded articular surface which fits 

 into a deep groove on the superior internal surface of mc. IV., thus 

 causing these bones to interlock at their proximal ends, though some- 

 what less perfectly than mcs. I. and II., and II. and III. The palmar 

 surface of mc. III. is rugose and there is a broad median ridge con- 

 tinued throughout the entire length of the bone. The distal end is 

 broad and deep, convex, and with an indistinct groove inferiorly. 



Metacarpal IV. is shorter and more slender than mc. HI. It is 

 greatly constricted medially and at the point of greatest constriction 

 it is nearly circular in cross-section instead of flat as in mcs. II. and 

 III. On the internal lateral surface of the proximal end there is the 

 deep groove mentioned above for the accommodation of a correspond- 

 ing prominence on the external lateral surface of mc. III. The 

 proximal articular surface is triangular. The lines bounding the in- 

 ternal and superior borders are of equal length and meet at right 

 angles so as to form the base and perpendicular of a right-angled tri- 

 angle, while the hypotenuse is formed by the line bounding the ex- 

 ternal lateral border. The latter, when this bone is placed in its nat- 

 ural position, runs obliquely downward and inward toward the median 

 axis of the foot. There is a broad, shallow emargination on the ex- 

 ternal lateral surface near the proximal end. The distal end presents 

 a broad and deep articular surface concave transversely and convex 

 supero-inferiorly. 



Metacarpal V. is shorter and stronger than mc. IV. It has some- 

 thing of the general shape of mc. I., though not nearly so massive as 

 that bone. It is compressed proximally, but expands distally. There 

 is a broad, rugose, concave surface on the internal side of the proximal 

 end. The proximal articular surface is crescentic in outline with the 

 upper arm heavier than the lower. There is a deep constriction on 

 the inferior side and another less pronounced on the superior just be- 

 hind the distal end. The distal articular surface is faintly convex and 

 subcircular in outline. 



The manner in which the different elements of the metacarpus in- 

 terlock at their proximal ends is suggestive af that which obtains in 

 the mammalia and is well calculated to give stability to the manus 

 when supporting the weight of the ponderous body. It will also, 



