42 



BULLETIN 110, UNITED STATES NATIONAL MUSEUM. 



The neural spines are large and robust. They gradually increase in height 

 from front to back, reaching their maximum development in the last dorsal (fig, 

 27). There is also an increase in the fore and aft diameter of the spines. 



Viewed from the side, the spines are narrower at the top than at the bottom: 

 The basal width is brought about by the development of thin marginal lamina-like 

 extensions of the spine. The posterior laminae turn backward and merge into the 

 surface above the posterior zygapophyses. Anteriorly they merge into the arch 

 posterior to and usually slightly above the level of the anterior zygapophyses. 



Between these laminae the median surfaces 

 both front and back are rugosely roughened 

 for ligamentious attachment. Above the mid- 

 height, this roughened median portion of the 

 spines extends forward and back respectively of 

 the side faces, which are smooth, in a gradually 

 narrowing axial area, being sharply defined both 

 front and back from the rugose central jDortion. 

 This roughening is by means of deeply pitted 

 projections and anastomosing channels run- 

 ning irregularly in a general vertical direction. 



The upper or distal ends have roughened 

 transversely expanded ends, and as in Gorgos- 

 aurus, and also in Tyrannosaurus the spines 

 have increased to such an extent in an anterior, 

 posterior direction as to approach one another 

 closely at the top. This development is most 

 prominently displayed in the eighth and tenth 

 of this series whereas in Gorgosaurus from the 

 fifth to the ninth and in Tryrannosaurus from 

 the seventh to the thirteenth. 



Fourteenth dorsal (No. 23). — The fourteenth 

 dorsal is so very much like the preceding ver- 

 tebra as to require but little description. -It is 

 the most robust element of the entire backbone. 

 The transverse processes are slightly shorter 

 than those immediately preceding it, and ex- 

 tend outward at right angles to the arch on 

 a nearly horizontal plane. The parapophysial 

 facet is smaller, and the roughened articular surface for the tuberculum of the 

 rib has changed to a more anterior position on the diapophyses, the face looking 

 forward and downward instead of directly ^lo^\•nward as in the anterior dorsal region. 

 In the last dorsal of No. 4734 the median wall between opposite sides of the cen- 

 trum is only 7 mm. in thickness. 



The principal dimensions of the two vertebral columns discussed above are 

 given in the table of measurements. 



Fig. 26.— Tenth dorsal vertebr.*. of Anteo- 

 DEMUS VALENS Leidt. No. 8367, U. S. N. M. i 

 NAT. SIZE. Viewed prom the right side, d, 



DIAPOPHYSIS; p, PAEAPOPHYSIS; Z, ANTEEIOE 

 ZTGAPOPHYSIS; Zg, ZYGOSPHENE; 2', POSTERIOR 

 ZY'GAPOPHYSIS. 



