MEGACEROPS TYLERI 451 



Breadth of shaft - 0.085 



Fore and aft diameter of shaft ----- .077 



The radius. — That of the left side is well preserved, except that 

 its distal end is somewhat weathered. It is not notably heavy, and 

 has a well-rounded shaft, but slightly compressed fore and aft at the 

 distal end. The radio-scaphoid facet is prolonged upward on the 

 posterior face, indicating a considerable range of flexion of the wrist. 

 The principal dimensions of the radius are : 



Length ---------- 0.490 



Antero-posterior diameter of mid shaft - .060 



Lateral diameter of mid shaft ------ .065 



Lateral diameter of lower end . 1 10 



The ulna. — The entire left and fragments of the right are preserved, 

 except for the distal end of the former, which is badly weathered. 

 The ulna is notable for its huge compressed olecranon, which widens 

 out distally into a heavy roughened tubercle. 

 The ulna measurements are as follows: 



Length (estimated) - - - - - - - - 0.620 



Antero-posterior diameter of olecranon from the humeral 



facet .17° 



Lateral diameter of olecranon tubercle - - - - .140 



Fore and aft diameter of mid shaft .080 



Lateral diameter of mid shaft ------ .080 



The manus (Plate IV, Figs. 1-3). — The general proportions well 

 shown in the figure, are somewhat broad rather than slender and in 

 direct correlation with the proportions of the skull. As has often been 

 stated, the manus shows some distinctly artiodactyl features, the most 

 notable being the retention of four digits with the main axis between 

 digits 3 and 4, rather than lying in the third itself. Another remark- 

 able feature is the extreme flexibility of the carpus, especially in the 

 development of a true ginglymoid joint between the proximal and 

 distal row of carpals. This is paralled in the carpus of Rangijer 

 caribou, and is quite distinct from the condition found in the horse 

 and camel, where, while the proximal facets of the distal carpalia 

 indicate a certain range of flexion, there is no development of special 

 pully-like ridges or keels, as in the titanothere and caribou. How 

 this articulation is formed in the rhinoceros and tapir the author 

 unfortunately has not had the opportunity to observe, but a compar- 



