No. i.] OSTEOLOGY OF PCEBROTHEIUUM. 35 



but narrow, that for the radius and ulna very small. In the 

 llama the pisiform has a much greater vertical depth and a 

 much less constricted neck ; the facet for the ulno-radius is 

 even larger than that for the cuneiform, and the whole bone 

 is longer, higher, and more compressed. 



The presence of the trapezium in the carpus of Pcebrotherium 

 is a very interesting fact, which was first demonstrated by Cope. 

 It is a very small bone of nodular shape, attached to the scaphoid 

 by a minute facet, and connected also with the trapezoid and 

 the rudimentary second metacarpal. Baur has shown (No. 1, 

 p. 117) that the trapezium probably still occurs sometimes in 

 the CamelidcB. 



The trapezoid is relatively smaller than in the recent genera, 

 and as in them shows no tendency to coalesce with the mag- 

 num. There is a single, slightly convex surface for articulation 

 with the scaphoid ; the surface for the magnum is not separated 

 into superior and inferior facets, as it is in the llama. Distally 

 there are two facets which meet at a very open angle : the larger 

 one is on the radial side, and is for the rudimentary second meta- 

 carpal ; the smaller one is for a process of the third metacarpal. 

 This is another example of Kowalevsky's "adaptive reduction." 



The magnum is broad and low, hardly more than half the 

 height of the unciform. The greater part of the proximal sur- 

 face is occupied by the facet for the scaphoid, which is flat in 

 front, but behind rises upon the convexity which articulates on 

 one side with the scaphoid and on the other with the lunar. 

 This convexity is decidedly more prominent than in the existing 

 genera. The anterior portion of the lunar facet slopes down- 

 ward at an open angle from the scaphoidal, and is decidedly 

 smaller. The distal surface for metacarpal III is nearly flat 

 and of triangular shape, with the apex behind. There is, of 

 course, no facet for mc. II, which is excluded from contact with 

 the magnum by the connection of No. Ill with the trapezium. 

 The posterior hook of the magnum has become rudimentary. 



The unciform is rather high and narrow, and so descends con- 

 siderably below the level of the magnum. The proximal surface 

 is unequally divided between the small oblique lunar facet and 

 the large transverse but sinuously curved cuneiform facet, but 

 the disproportion is not nearly so striking as in the modern 

 genera. In the llama, for example, the cuneiform facet is many 



