'52 



UNGULATES. 



In all the Ungulates the limbs have entirely ceased to be used as organs of 

 prehension, and there would seem to be no necessity why there should be any 

 adherence to the primitive five-toed type, as development advances. The majority 

 of the members of the order being, however, unable to protect themselves against 

 foes, and being also, in proportion to their height, heavy-bodied animals, the attain- 

 ment of a high degree of speed was essential to their well-being and development, 

 if not for their actual existence. For such a kind of life it will be obvious that 

 the greater the length and slenderness of limb, the greater will at first sight be the 

 speed. Now, in order to produce a long and slender, and at the same time a strong 

 limb, from a stout and short-toed one, greater strength will clearly be attained by 

 reducing the number of the toes, and lengthening and strengthening those which 

 remain, rather than by lengthening the whole of the five 

 toes, the slender bones of which would be liable to fracture 

 by the concussion of the solid hoofs against the ground. 

 Accordingly, among the Ungulates, the plan has been to 

 gradually lengthen and strengthen the bones of one or more 

 of the original five toes, and at the same time to dispense 

 more or less completely with the others. In almost the 

 lowest Tertiary rocks of Europe and North America there 

 occur, for instance, the remains of certain large Ungulates, 

 known as coryphodons, in which both the fore and hind-feet 

 (as represented in the accompanying figure) have five com- 

 plete toes. It will be observed that both the metacai-pal 

 bones and the toe bones by which they are succeeded are very 

 short ; and these animals must accordingly have walked to a 

 certain extent upon the soles of their feet in the old-fashioned 

 plantigrade manner. 1 It will also be noticed that the third 

 or middle toe (ill) is larger than either of the others, and symmetrical in itself. 

 Another feature of this type of foot is that the component bones forming the two 



horizontal rows of the wrist are placed almost verti- 

 cally one above another, the bone lettered I merely 

 touching the adjacent angle of the one marked u. 

 When we ascend to the overlying Miocene 

 Tertiary deposits we meet with other large 

 Ungulates having a foot of the type of that 

 shown in our second figure, where it will be 

 noticed that while all trace of the first toe (i) has 

 disappeared, the metacarpal bones of all the others 

 have become very much more elongated, in con- 

 sequence of which the animal no longer walked 

 upon the soles of its feet, but entirely upon the 

 toes, or was, in other words, digitigrade. It will 

 also be observed that the third toe has become 

 still larger in proportion to the others. Moreover, the upper row of wrist-bones 



1 As a matter of fact, the coryphodon was partially digitigrade in its fore-feet, but entirely plantigrade in the 

 hinder ones. 



BONES OK THE LEFT WRIST 

 AND FORE-FOOT OF THE 

 coryphodon (J nat. size). 



The letters indicate the 

 bones of the wrist (cuneiform, 

 lunar scaphoid, trapezium, 

 trapezoid, magnum, unciform), 

 and the numerals those of the 

 metacarpus. — After Osborn. 



BONES OF THE LEFT WRIST AND FOOT OF 



the titanothere (J nat. size). — After 

 Osborn. 



