TRIPLOPGS. 683 



Vertebrce. — The atlas is about as long relatively as that of the horse. 

 Its transverse processes have moi'e anteroposterior than transverse extent. 

 The summit of the neural arch has a median ridge separating two grooves. 

 The inferior surface of the centrum has a nearly median, obtuse hypapo- 

 physis The axial facets are well separated below. The vertebrarterial 

 canal pierces the base of the transverse process behind and below, and 

 notches it deeply anteriorly. Above this notch the usual perforation of the 

 arch is present. The axis is not relatively quite so long as that of the 

 horse; it is a little longer than in Hyrachyus eximius, but ratlier shorter 

 than in Hyracodon arcidens (PI. CII, Fig. 7). The atlantal facets are spread 

 well apart, and the articulating surface of the odontoid does not connect 

 with them. The latter is rather long, is obtuse, and slightly recurved; it 

 has no raised borders. Between the atlantal faces the inferior surface is 

 plane. Posterior to this the middle line bears a prominent keel. The dia- 

 pophyses are long, narrow, and recurved, and each is pierced at the base 

 by the vertebrartei'ial canal. The posterior articular face is but little con- 

 cave, and a little oblique, and is a little wider than long. 



The succeeding cervicals regularly diminish in length, and become 

 more strongly opisthocoelous, the seventh having quite a ball in front. The 

 sixth has a slender diapophysis directed posteriorly, and quite distinct from 

 the wide and long parapophysis which is directed downwards and out- 

 wards. The posterior angle of the latter extends as far back as the cen- 

 trum. The seventh has only a flat transverse diapophysis. The first 

 dorsal has a very stout diapophysis excavated below for the rib tubercle. 

 The diapophyses of the third and fourth dorsals are not so stout. The 

 capitular fossae are large. The centra of the anterior dorsals are flattened 

 below ; they are concealed in part by the matrix in this specimen. The 

 neural spine of the sixth cervical is narrow, and is directed forwards. 

 That of the seventh is vertical, and narrows rapidly from a base which is 

 rather wide anteropostexiorly. The spines of the dorsals are wider, and 

 are directed gently posteriorly ; they are probably long, judging from the 



size of their bases. 



Measurements of vertebrce. 



M. 



Length centrum of atlas on side 027 



Length centrnm of atlas below 010 



