176 COPE. [Vor. IIT. 
to the former, outwards on each other. Beyond the point of 
vertical suspension the strain on the heads of the metacarpals 
presses them outwards, thus antagonizing the effect of the in- 
ward pressure. The linear relation therefore remains unaltered, 
SO GTI a 
Figure 19. — Simia nigra, carpus one-fourth the nat. size. 
Figure 20.— Bradypus tridactylus, carpus one-fourth nat. size. 
In the sloth (Aradypus tridactylus), which also progresses in 
suspension, the rotation of the radius and manus is far less 
considerable than in Simia; is in fact almost wanting. In pro- 
gression the strains are alternately opposite each other at the 
cubito-carpal articulation, and as a consequence the scaphoid and 
cuneiform are subequally developed and at the expense of the 
distal part of the lunar. The equality of these opposed strains 
is also represented by the similarity of the articular surfaces 
between the scaphoid and trapezoido-magnum, and the cunei- 
form and unciform (Fig. 20). 
I can offer no plausible theory to account for the diplarthry 
of the human carpus. The movements of the human hand are 
so many and various that the explanation of its carpal structure 
is a most complex proposition (Fig. 1 B, p. 150). 
An especial peculiarity characterizes the cubito-carpal and 
intercarpal articulations of the Anthropomorpha, Quadrumana, 
and sloths. Both of these articulations are strongly convex 
proximally, offering halves of ball and socket joints. In the 
intercarpal articulation the articular surface covers a large ante- 
rior face of the magnum and unciform bones. This form is 
represented by a trace only in Ungulates. Its function evi- 
