368 Annals of the Carnegie Museum. 



to the internal margin and internal articular surface of the radius 

 with which during the life of the animal it probably had a direct, car- 

 tilaginous articulation. The external lateral margin of the proximal 

 end is regularly concave and just in front of the articular surface there 

 is a deep cavity for the reception of a corresponding prominence on 



mil 



Fig. II. Dorsal view of metacarpals of right manus placed side by side in regu- 

 lar order, about one-tenth natural size. (No. 563.) 



the internal margin of metacarpal II. The external surface is rugose 

 throughout the entire length of the bone ; it is much constricted ver- 

 tically in the middle, but with decided distal and proximal expan- 

 sion for contact with metacarpal II. The internal lateral surface 

 is regularly but gently convex vertically throughout the entire length 

 of the bone and only slightly constricted vertically in the middle 

 region. The superior surface gradtially broadens from the proximal 

 to the distal end. The inferior surface is deeply concave longitudi- 

 nally, broad at the distal extremity, but reduced to a sharp narrow 

 ridge at the proximal end. The distal articular surface has the verti- 

 cal and transverse diameters subequal. It is continued well back on 

 the palmar side of the bone in order to accommodate the thin sheet 

 of bone which projects posteriorly from the palmar side of its proximal 

 phalanx. There is a vertical, median groove for the accommodation 

 of the low median keel of the latter. 



Metacarpal II. is longer and more slender than the preceding, al- 

 though decidedly stronger than metacarpal III. It is somewhat con- 

 stricted medially both in its vertical and lateral diameters. Compared 

 with metacarpal I. it is broad, but greatly depressed. The superior 

 as well as the distal portions of the lateral surfaces are smooth, while 

 the inferior and proximal portions of the lateral surfaces are covered 

 with rugosities. The inferior internal angle of the proximal end of 

 this bone is especially modified so as to fit nicely into the deep cavity 

 just described as present on the external lateral surface of metacarpal 



