350 



M. S. Lull — Pleistocene Ground Sloth 



large foramen is seen in the center of the neural aspect. The 

 anterior and posterior faces of the centrum, although the 

 epiphyses are absent, give evidence of having been slightly con- 

 vex with a depression in the center of each. The lateral 

 aspects are each concave along the antero-posterior axis and 

 there is a long straight depression having a width of about 5 mm , 

 which runs from below upward and slightly backward across 

 either side of the centrum. This mark is also discernible on 

 five other centra among those preserved, although sometimes 

 upon one side only; it is again somewhat variable in position. 



Fig. 6. 



Fig. 6. Seventh ? dorsal vertebra of Mylodon harlani. One-fourth nat. 

 size, a, anterior, p, posterior, and I, left lateral aspects ; cf, capitular rib 

 facet ; tf, tubercular facet ; other lettering as in fig. 4. 



The neural canal is large and elliptical in outline, with the 

 long axis, which is greater than the width of the centrum, 

 horizontal in position. The neural arch arises from the ante- 

 rior half of the centrum and juts forward to bear the rib facet 

 and to support the prezygapophyses. The latter are borne 

 entirely upon the broad roof of the neural arch, while the post- 

 zygapophyses lie upon the under side of the roof where it nar- 

 rows into the spine. The latter commences as a low ridge at 

 the extreme anterior margin of the neural arch as preserved, 

 rising gradually at an angle of only 25° above the horizontal 

 plane. The transverse processes are heavy, rugose at their 

 extremity, and bear a small tubercular rib facet on their outer 

 aspect. The capitular rib facets are two on a side, a relatively 



