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TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



The vertebral formula is cervicals 7, dorsals 17, 

 lumbars 3(?), sacrals 4, caudals 20 + . In detail 

 the vertebrae resemble those of B. rohustus more than 

 those of Menodus giganteus, but they are clearly dis- 

 tinguished in many characters from both species. 



Adaptive provision for the insertion of. a powerful 

 ligamentum nuchae correlated with the heavy skull 

 is seen in the great rise of the four anterior dorsal 

 spines, which are subequal in length, with their very 

 rugose superior extremities and triangular basal por- 

 tions fitted to resist the strain of the neck muscles. 

 The neck is short but moderately flexible; the back is 

 short, the tail greatly reduced. 



The detailed characters of the presacral vertebrae 

 are best illustrated in Plates CXCV-CC, which were 

 drawn with such accuracy that most of the measure- 

 ments can be taken from them. In the following 

 description comparison is made throughout with the 

 type of Brontops rohustus. 



The massive atlas measures 440 millimeters across 

 the pleurapophyses, which are prominently convex 

 (unlike the type of B. rohustus) at the extremities; 

 inferiorly the vertebrarterial canal traverses a broad 

 (54 mm.) bridge; the hypapophysis is tuberous; 

 the neural spine is prominent and bifid. The axis 

 exhibits atlanteal facets 235 millimeters in width; 

 the vertebrarterial canal traverses the central portion 

 of the platelike pleurapophysis (the lower portion in 



B. rohustus) ; the superior border of the spine is some- 

 what indented anteriorly and broadly tuberous 

 posteriorly. In cervicals 3-7 the pre- and postzyga- 

 pophyses face obliquely inward and outward, re- 

 spectively, as in B. rohustus; the superior and inferior 

 laminae of the transverse processes differ considerably 

 in detail from those of B. rohustus, as seen by compar- 

 ison of Figure 618 and Plate CCXXIX. In the ribless 



C. 7 the spine suddenly increases in height to about the 

 same proportions as that of B. rohustus. The cervical 

 centra are deeply opisthocoelous, the transverse and 

 vertical diameters being about ecjual. 



The first dorsal is distinguished from that of the 

 type of B. rohustus by the fact that the postzyga- 

 pophyses are subhorizontal as in the succeeding dor- 

 sals, whereas in B. rohustus the postzygapophyses of 



D. 1 and the prezygapophyses of D. 2 are transversely 

 oblique, resembling those of the cervicals. The neural 

 spines of dorsals 1-17 are characteristic; the spine in 

 D. 1 is greatly elevated and transversely compressed; 

 the spines of D. 2, D. 3, D. 4 are subequal in height, 

 gradually expanding into broad rugosities at the tips; 

 the triangular basal portion of the spine, with its pos- 

 terior groove, rises rapidly from D. 1 to D. 4; at the 

 same time the spines diminish rapidly in anteropos- 

 terior diameter, and this diminution proceeds as far 

 back as the spine of D. 14, behind which the spines 

 increase again in anteroposterior diameter into the 

 lumbar region. The zygapophyses, beginning with 



the postzygapophyses of D. 1, lie in subhorizontal 

 planes as far back as D. 11, thence shift to transversely 

 oblique planes D. 12-D. 14, and into nearly vertical 

 planes, D. 15-D. 16. The zygapophysial facets of D. 

 17 and L. 1 are distinguished from all others by being 

 concavo-convex but not revoliite as in Palaeosyops. 

 The diapophyses, or attachment of the tubercles of 

 the ribs, pass from broadly expanded plates in D. 1 

 backward into tuberosities of diminishing size in D. 11, 

 and above these tuberosities they rise in D. 12-D. 17 

 into distinct vertical processes. The capitular facets 

 are borne largely on the posterior faces of the centra 

 and in a less degree on the anterior faces, throughout 

 as in B. rohustus, rising gradually to the upper sides 

 of the centra. 



Three lumbars, although somewhat crushed later- 

 ally, afford all the principal characters. They exhibit 

 stouter spines and transverse processes than in B. 

 rohustus. The postzygapophyses of L. 1 and the 

 prezygapophyses of L. 2, although vertically placed, 

 have a convexo-concave articulation like that between 

 D. 17 and L. 1; in L. 2 and L. 3 the zygapophysial 

 facets are flattened or plane and placed in oblique 

 planes. 



The caudals are added from another individual, and 

 neither the specific determination nor the enumera- 

 tion is certain. C. 2 is represented with a chevron, 

 and this, as Hatcher has pointed out, may be an 

 error; the first chevron may occur below C. 3, as 

 in B. rohustus. The centra are typically biconvex, 

 increasing in length from 40 millimeters in C 1 to 

 60 in C. 8. The bifid spines and the vestigial zyga- 

 pophyses persist in C. 1-C. 9; the transverse processes 

 subside in the same vertebrae. 



The ribs are admirably preserved in a continuous 

 series on both sides. The general characters are as 

 follows: Ribs 1-5 progressively increase in length 

 and width of section anteroposteriorly; ribs 5-8 are 

 of approximately equal length but slightly decrease 

 in anteroposterior measurement; ribs 9-17 decrease 

 in length, also in anteroposterior diameter or width; 

 they increase in the convexity of the outer surface, 

 passing from a more flattened to a more convex, 

 lenticular section. The measurements may readily 

 be taken from the restoration except those of R. 1 

 (445 mm.), R. 2 (555 mm.), and R. 3 (625 mm.). 



As compared with the Eocene titano there PaZaeosyops 

 the tubercles are less widely separated from the heads, 

 this being correlated with the less extreme transverse 

 extension of the diapophyses. The large size of the 

 ribs, the persistence of tubercles posteriorly, the 

 abbreviation of the lumbar region all indicate an 

 enormously capacious chest and abdominal cavity. 



Two of the mid-sternebrae are preserved. They 

 are laterally compressed, with flaiing articular surfaces, 

 concave superior and convex inferior surfaces; the 

 most anterior, which may represent the second 



