Nodosaurus textilis Marsh. 



103 



coossified that the line of demarcation between the 

 successive vertebrae is practically obliterated; there is 

 generally not even the usual dilatation at the articular 

 ends of the centra to betray their limitations. Ventrally 

 they are characterized by a median longitudinal groove, 

 which is continued throughout the entire known series 

 of caudal vertebrae as well. The anterior centra (sacro- 

 lumbars) are relatively long and slender, broadening 

 posteriorly. The three primary sacrals bear heavy 

 sacral ribs, the rounded lower margins of which are at 

 the same level as that of the centra from which they 

 arise. The expanded ends of the sacral ribs abut against 



Fig. 2. — Dorsal vertebra of Nodosaurus textilis. A, left lateral, B, an- 

 terior aspect. One-fifth natural size. &, actual bone of centrum; c, cen- 

 trum; cp, costal (armor) plate; d, diapophysis ; icp, intercostal plate 

 (seen beyond the costals) ; nn, matrix impression of centrum; yo, postzyga- 

 pophysis; pr, prezygapophysis ; r, rib; s, spinous process; t, longitudinal 

 tendon. 



the inner wall of the acetabulum, and the first two are 

 more massive than the third. Dorsally- these ribs are 

 continuous with the diapophysial lamina, of which the 

 horizontal upper plate passes into the surface of the 

 ilium as seen from above (pi. II). The ribs borne on 

 the four presacral elements are comparable except for 

 their much greater slenderness. There is, as with the 

 true sacrals, an expanded horizontal diapophysial 

 lamina, especially near the vertebra and beneath the 

 overlying armor. This arises, as does the rib, from the 

 neural arch. Beneath this lamina, and united with it, 

 without line of demarcation, lies the slender rib, the 

 expanded horizontal portion extending at first entirely 



