742 



THE UNGULATES, OR HOOFED MAMMALS 



any adherence to the primitive five-toed type, as develop- 

 ment 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 attainment of a high degree of speed was essen- 

 tial 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 



BONES OF THE LEFT greater will at first sight be the speed. Now, in order to 

 WRIST AND FORE-FOOT produce a long and slender, and at the same time a strong 

 OF THE CORYPHODON. limb) from a ^ Q ^ and s h O rt-toed one, greater strength will 



(One-fourth natural size.) , , '... u r ^t. j 



clearly be attained by reducing the number or the toes, and 



The letters indicate the bones 



of the wrist (cuneiform, lunar lengthening and strengthening those which remain, rather 



scaphoid, trapezium, trapezoid, . ',, - . , ,, ,,111 



magnum, unciform), and the than by lengthening the whole of the five toes, the slender 



pr-Af'ter o s e born hemetacar " 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 low- 

 est 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 complete 

 toes. It will be observed that both the meta- 

 carpal bones and the toe bones by which they 

 are succeeded are very short; and these animals 

 must accordingly have walked to a certain ex- 

 tent upon the soles of their feet in the old- 

 fashioned plantigrade manner.* It will also be 

 noticed that the third or middle toe (in) is 

 larger than either of the others, and symmet- 

 rical 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 vertically one above another, the bone lettered / 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 appears to have been slided over those of the lower 



*As a matter of fact, the coryphodon was partially digitigrade in its fore-feet, but entirely plantigrade 114 

 the hinder ones. 



BONES OF THE LEFT WRIST AND FOOT 

 OF THE TITANOTHERE. 



(One-eighth natural size.) 

 (After Osborn.) 



