Mylodon h avian i, from Rock Creek, Texas. 351 



large anterior one borne partly on the centrum but mainly on 

 the neural pedicel, while the posterior facet is small though 

 the loss of the epiphysis probably reduces its area. As pre- 

 served its lower limit is horizontal with that of the anterior 

 facet. The intervertebral foramen is very large, in keeping 

 with the dilated neural canal and implying the innervation of 

 large muscles and other organs in the neighborhood of the ver- 

 tebra under discussion. 



Dimensions. 



Centi urn, length (estimated ) 54mm 



breadth over rib facets _ 78 



depth .. _ 51 



Neural canal, height 46'5 



breadth 57 



Neural arch, ant. -post, diameter 70 



width over zygapophyses (estimated). 90 



Width over transverse processes __ 154 



Total length preserved of spinous process . _ . _ 130 



Total height of vertebra 145 



Caudals. — Of the anterior caudals, seven are preserved out 

 of an estimated twenty-one, one-third the number but con- 

 stituting nearly half the total length of the tail. 



Proximal caudal. — What is apparently the proximal caudal 

 is present and well-preserved, lacking only the transverse pro- 

 cesses. It is a massive bone, with low neural arch and well- 

 developed articulations. The centrum is somewhat pentagonal, 

 this time with a well-developed keel-like ridge with a nutritive 

 foramen on either side on the neural aspect, and a concavity 

 below. The anterior articular face is convex, with a slight 

 median depression, while the posterior face presents a peculiar 

 curve in that the central depression seems to be prolonged 

 horizontally across the entire face, owing to the development 

 of a low prominence toward each upper lateral angle. Ven- 

 trally articular facets for the hsemapophyses or chevron bones 

 are present, though small compared with those of more pos- 

 terior vertebrae. They also contrast with the latter in being 

 connected with each other and with the base of the transverse 

 process by a flat bridge of bone which forms a canal passing 

 obliquely downward, backward and inward, suggestive of the 

 vertebrarterial canals of the cervical vertebrae. In the other 

 caudals the chevron facets are borne on separate pedicels, the 

 canal being at most but a deep and well-marked groove. The 

 neural arch is very heavy and the pedicels especially are so 

 broad and massive that both the neural and intervertebral 



