Peterson: Oste(m.ogy or Oxndacivix's. 447 



posterior ilorsals, with the complete himbar region and sacrimi, all in 

 position and articulated by their zygapophyses save at the break in the 

 dorsal region affords additional evidence as to the vertebral formula. 



The Atlas. — (PI. V, Fig. i.) The atlas is proportionally long 

 and narrow, in this respect more nearly resembling Po'cbrotlierium 

 than the recent camel or the llama. The articulations for the occipital 

 condyles are deeply concave, almost meeting inferiorly in the median 

 line. Superiorly the notch is proportionally much narrower and some- 

 what deeper than in the recent forms. Externally each cotylus is 

 notched like that of the recent Tylopoda. The dimensions of the 

 cotylus are nearly alike in O. longipes and the specimens of the llama 

 here used for comparison. The neural arches are also approximately 

 of the same height. The spine is rudimentary as in the living genera. 

 The keel on the inferior arch well developed but does not extend to 

 the posterior margin as it does in the llama. There is a deep de- 

 pression on either side of the median keel, which takes up the entire 

 inferior surface of the atlas. Articular surfaces for contact with the 

 accessory facets of the basi-occipitals are present on the anterior sur- 

 face of the inferior arch, though absent in Pocbrotheritnn.^ The arti- 

 culation for the axis extends higher up on the arch and is compara- 

 tively narrower than in the recent camel and llama. This articulation 

 is more vertical than in the llama and is quite distinct from that in 

 any of the living forms. 



Another character distinguishing the ])resent genus from the recent 

 camels is the posterior prolongation of the al^. This seems to be the 

 condition also in the other genera of the Loup Fork camels. In 

 other respects the transverse processes are similar to those in the atlas 

 of the recent camel and the llama. The foramen for the superior 

 branch of the first spinal nerve compares well with that of the recent 

 genera. Its posterior opening is located at the base and on the dorsal 

 side of the transverse process. 



The Axis. — (PI. V, Fig. 2.) There is a striking similarity in 

 the height and position of the neural spine and the shape of the 

 odontoid process in the axis of Oxydactylus longipes and that of the 

 recent camel. The spine overhangs the neural canal anteriorly as in 

 the recent camel and extends backwards and gently upwards to the 

 extreme i)Osterior, border of the neural arch terminating above in a 

 heavy and rugose tubercle. In the llama the si)ine does not over- 



^ fonrn. Morph., Vol. V, Xo. I, p. 28. 



