70 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 20, 



almost entire from the septarian nodule, was of the left leg ; its 

 length is 4 inches 9 lines. The proximal articular surface, PI. IV. 

 fig. 11, is more equally triangular than in Palaotherium. The outer 

 facet is slightly convex ; the inner one slightly concave transversely. 

 The back part of the proximal end of the bone, fig. 10, shows a 

 broad and deep concavity, bordered by sharp margins ; the outer 

 part is somewhat less concave ; the inner part is slightly convex ; 

 the rotular ridge was not extracted entire, but was evidently well de- 

 veloped, and extended an inch and a half down the bone. The most 

 characteristic feature of the tibia is the articular surface at the distal 

 end, fig. 13, of which sufficient is preserved to show the obliquity of 

 its course across that end, corresponding with the obliquity of the 

 articular trochlea of the astragalus which is common to the odd-toed 

 hoofed quadrupeds. From these the even-toed group are distin- 

 guished by the rectangular disposition of the ankle-joint. 



Metatarse: PL IV. fig. 14. — The portion of matrix containing 

 the part of the calcaneum, c, and three metatarsals, shows the latter 

 dislocated, and with only one articular end entire — the lower one — 

 in one of them. This is, however, as characteristic as any of the 

 distinctive features of the before-described bones, by the unsymme- 

 trical form of the distal trochlea, due to the position of the ridge 

 near one of the borders of the bone. Both this configuration and 

 the position of the metatarsal show it to have been the outermost of 

 the three : the proximal end is broken off : the length of the bone 

 preserved is 1 inch 5 lines. Of the mid-metatarsal only a small part 

 is exposed, from which the articular end is broken away. Of the 

 innermost metatarsal 1 inch 8 lines is exposed, but both articular 

 ends are wanting. The difference in the diameter of the three meta- 

 tarsals is less than in the Palceotherium, the middle one being only 

 very little thicker than the other two. In the Tapir the middle 

 metatarsal is less expanded than in the Palceotherium. In the Hy- 

 rax the three metatarsals are of equal thickness ; and the Pliolophus, 

 and probably other Lophiodonts, thus resemble the Hyrax and Tapir, 

 more than the Palceotheria did. 



Remarks on the Bones of the Extremities. — On a retrospect of the 

 characteristics of the limb-bones above described, it will be seen that 

 the humerus testifies to the ungulate character, and the bones of the 

 hind-leg to the perissodactyle modification, of Pliolophus, with a de- 

 monstration that the odd number of hind-toes was " three " instead 

 of "one" or "five." 



The great size, position, and altitude of the proximal tuberosities 

 of the humerus, with the shape of the sessile head of the bone, indi- 

 cate the limited extent and direction of motion of the humerus, and 

 that it belonged to a limb not capable of being rotated or bent out- 

 ward, as in the action for seizing, striking, climbing, or burrowing. 

 The comparatively small size of the distal end, and the little-deve- 

 loped supinator ridge equally indicate the want of size in the supinator 

 or pronator muscles in a limb where the rotation of the wrist or the 

 fore-arm is abrogated. The third trochanter on the femur, the oblique 



