70 SCOTT. [Vol. V. 



imal end of mt. II is clearly a part of the cannon-bone, form- 

 ing a large facet for the ento-cuneiform ; its line of suture 

 with mt. Ill is still visible. A comparison with the modern 

 forms shows that in them also this bone is preserved, as Boas 

 (No. 3, p. 52) and Gaudry (No. 12, p. 117) have found to be the 

 case in the true ruminants. I find, however, no trace of mt. 

 V, and from its altogether lateral attachment to the cuboid in 

 Pcebrotherium it appears probable that it has entirely disap- 

 peared. 



The changes in the structure of the hind limb from Pro- 

 camelns to the recent genera are not sufficiently important to 

 call for description. 



The Phylogeny of the Tylopoda. 



The immediate ancestors of the modern Camelida are, unfor- 

 tunately, not known to us, though the ProtaucJieuia of Branco 

 (No. 4, p. no) not improbably stands in this relation to the 

 llama series, the forms which occur in the Pliocene of the 

 United States being highly specialized side branches, which 

 have died out without leaving successors. Toward the end of 

 the Miocene the ancestors of the modern forms probably mi- 

 grated from North America to South America and the Old 

 World, as is indicated by the Siwalik fossils and others. In 

 the upper Miocene, or Loup Fork beds, we meet a large number 

 of species of this group. Homocamelus, so far as known, is very 

 camel-like, and it might seem at first sight that we have here 

 a direct ancestor of the camels ; but the peculiar and reduced 

 character of the premolars, though still present in full numbers, 

 renders it probable that this genus is not in the direct line, but 

 is perhaps the forerunner of Holomenisciis or Eschatius. Pliau- 

 cJienia has frequently been regarded as the forerunner of the 

 llamas, but the known remains of it are altogether too imperfect 

 to enable us to form a decision on this question, and the great 

 shortening of the disastema would seem to oppose this view. 



Procamelus, on the other hand, if not itself the common 

 ancestor of the two recent lines, obviously stands very near to 

 their point of divergence. It may be objected that this genus 

 has already become too highly specialized in both directions to 

 be the ancestor of either series ; e.g. agreeing with the llama in 



