THE MAMMALIA OF THE DEEP RIVER BEDS. 113 



in the Sleinheim specimens they seem even to be enlarged. (/) The median ungual 

 phalanges are much elongated, but in most forms of the genus they are much de- 

 pressed and flattened and have gained but little in vertical diameter. 



Some of the species of Miohippus already point in the direction of Anchitherium, 

 as we have seen to be the case in regard to the inner cusps of the lower teeth. The 

 typical form of ungual phalanx in the John Day genus is that of M. anceps as figured 

 by Marsh (No. 27), in which that of the middle digit is relatively short and differs 

 but little from the hoof of Mesohippus, but in a specimen obtained by the Princeton 

 party of 1889 on the Middle Fork of the John Day river, in eastern Oregon, this 

 phalanx is very much elongated, depressed and narrowed, so as to recall in a striking 

 manner the corresponding bone of Anchitherium (see PI. II, Fig. 1G). As this speci- 

 men is not accompanied by teeth, I cannot yet refer it to any described species of 

 Miohippus, but that, in one respect at least, this species tends strongly towards An- 

 chitherium is obvious. There remains, however, one point as to which there is much 

 uncertainty. In A. aurelianense the meso- and ectocuneiforms arc co'Jssified, while 

 in all other equities in which the tarsus is known the external cuneiform is free and 

 the median united with the internal. Kowalevsky does not state how many speci- 

 mens he was able to examine, and thus to determine whether the condition which he 

 describes in the French forms is the invariable rule or only an occasional variation, 

 such as Forsyth Major has shown to occur not very infrequently among recent horses 

 (No. 15, p. 63). Unfortunately, nothing is known as to the condition of the tarsus, 

 in this respect, of the specimens from Steinheim and of A. equinum. 



Until the question is determined as to whether the coalescence of the meso- and 

 ectocuneiforms be the normal condition in Aichitherium, it is useless to speculate on 

 the way in which this peculiarity was brought about, but a hint of the possible 

 method is given by the specimens shown in PL II, Fig. 15, which is of a White 

 Eiver Mesohippus. In this animal all three cuneiforms have coalesced into a single 

 piece, which may possibly have been the first step, to be followed later by a separa- 

 tion of the internal element. That this particular case is perhaps pathological, is 

 indicated by the ankylosis of the second and third metatarsals, or it may be due 

 merely to age, as there are no exostoses in the joint. Nevertheless, the specimen is 

 not without suggestive value, and the example of the recent horses shows us that 

 such changes may and do take place in the individual. Another indication that 

 variations looking to Anchitherium were commenced as early as the genus Mesohip- 

 pus, is afforded by the curious species of that genus, M. {Anchitherium) cuneatus 

 Cope, to which Prof. Cope has called my attention. This species displays a strong 

 tendency to assume the concave and inwardly projecting external crescents of the 



