90 



THE MERYCOIDODONTID/E 



borders of the posterior articular surfaces, for the heads of the ribs, are ovate, with the greater 

 diameter vertical. 



The cervical and first two dorsal vertebra; of Cat. No. 13118 are articulated and bent back- 

 ward to the most extreme position possible without disarticulation, caused in all probability by ordi- 

 nary postmortem desiccation. 



The dorsal centra (Fig. 52) are relatively long and medially constricted. Ventral spines 

 (hypapophyses) are absent. The anterior articular processes are nearly circular. The posterior 

 articular processes are elliptical and centrally depressed. The arch is not perforated by a foramen 

 on the side, because there is no posterior root of the arch to enclose the foramen. In other words, 

 it is an open canal, instead of being enclosed by a bridge of bone. There is no foramen in the 

 posterior parts of the roots of the transverse processes. There are metapophyses on all the dorsal 

 vertebra;, except the first, and in the posterior five or six they project from the anterior articular 

 processes. The dorsal spines are broad and long. They extend backward to the eleventh vertebra, 



Fig. 52. — Eforeodon 

 socialis Marsh. First dorsal 

 vertebra. CT. Cat. No. 

 13119 Y.P.M. 



Fig. 5 3. — Eforeodon 

 socialis Marsh. Fifth lum- 

 bar vertebra. CT. Cat. 

 No. 13119 Y.P.M. 



Fig. 54. — Eforeodon 

 socialis Marsh. Second 

 caudal vertebra. CT. Cat. 

 No. 13119 Y.P.M. 



Fig. 5 5. — Eforeodon 

 socialis Marsh. Thirteenth 

 caudal vertebra. CT. Cat. 

 No. 13119 Y.P.M. 



All 1/2 nat. size. (After Thorpe, 1931.) 



which may be termed the "anticlinal vertebra" or "center of motion." These spines diminish in size 

 posteriorly to about the eleventh. The superior edges of the spines are slightly enlarged. 



The shape of the neural canal is slightly more elliptical than round in cross section, with the 

 greater diameter vertical. The anterior articular surfaces are slightly oblong, but in a transverse 

 direction. 



In the seventh dorsal the shape of the neural canal has changed very markedly, so that it is 

 now horizontally elliptical. In none of the dorsals is the intervertebral canal posteriorly closed. 



The lumbar vertebra; (Fig. 53) number six. The centra are longer than those of the dorsals 

 and, in the latter, have a ventral crest. The notches at the posterior bases of the arches become 

 progressively greater toward the posterior of the series. Superiorly the arches are not deeply 

 notched. The metapophyses are well defined and extend outward and backward. The transverse 

 processes are nearly equal in length and width throughout the series. They do not bend downward, 

 nor do they flare outward at their distal extremities. They do not articulate with the sacrum. The 

 dorsal spines are thin and broad and incline forward, except the last, and are nearly equal in height. 

 The tongue and groove articulation of the lumbar zygapophyses is well developed, suggestive of 

 that of the creodonts. 



The sacrum consists of four ankylosed vertebras, to which the first caudal is united in this 

 specimen. The first vertebra and anterior part of the second were joined to the ilia by an articula- 

 tion and the others to the ischium by very strong ligaments. The sacrum is but slightly curved. 

 The spines are well developed, gradually diminishing in size, but are still decidedly broad in the 



