594 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 49. 



VERTEBRA OF THESCELO 

 SAURUS NEGI.ECTUS GlL- 



MORE. Type. No. 7757, 



U.S.N.M. J NAT. SIZE. 



Lateral view, d, Dia- 



POPHYSIS; p, PARAPOPHY- 



si.s; s, SPINOUS process; z, 



ANTERIOR ZYG apophysis; 

 Z', POSTERIOR ZYGAPOPHY- 



SIS. 



border of the transverse process and approaches the tuberculum until 



on the fourth vertebra in front of the sacrum there is but a single 

 facet on the end of the exceedingly heavy proc- 

 ess (see d, fig. 5). This vertebra, as in the re- 

 maining dorsals, all carry single headed ribs. 

 The transverse processes of the anterior dor- 

 sals are directed upward at an angle of more 

 than 45°, so that when 'viewed from the side 

 they appear to equal the spinous process in 

 height, as shown in figure 3. Proceeding poste- 

 riorly the upward inclination becomes less and 

 less until in the posterior dorsals it extends out 

 nearly horizontal (fig. 5). Throughout the series 



Fig. 4.— Eighth presacral the point of Origin of the transverse processes 

 is especially low down on the arch, though 

 higher in front than behind. 



The spinous processes are thin rectangular 

 plates of bone (figs. 4 and 5), with but little 

 transverse expansion of their upper extremities. 

 These gi-adually increase in height posteriorly, 

 reaching their maximum development in the 



last dorsal (first presacral). The last dorsal (or sacro-dorsal) may 



be distinguished by its greater bulk and 



especially by the great transverse diameter 



of its posterior end. It is the largest 



vertebra of the entire vertebral column. As 



in aU known dinosaurs, there are no true 



lumbar vertebrae, as all bear ribs. The 



average intercostal space between the dor- 

 sal vertebrae, as found articulated, is about 



5 mm.. 



Sacrum. — The sacrum, as in Hypsilojjhodon, 



consists of five vertebrae that are directly 



united with the Uia by sacral ribs. These ver- 

 tebrae are suturally united and appear to be 



firmly anchylosed. Sacral one may be dis- 

 tinguished from those that follow by the gi-eat 



transverse expansion of the anterior end of its 



centrum. The second sacral has the smallest 



centrum of the five and in cross-section is 



subcircular. The remaining three are more 



broadly rounded and but shghtly concave 



antero-posteriorly. The fu-st two sacral ribs 



unite with the centra intervertebrally, but the remaining tliree 



articulate laterally with their respective centra (fig. 17). 



Fig. 5.— Third presacral ver- 

 tebra of Thescelosaurus 

 neglectus Gilmore. Type, 

 No. 7757, U.S.N.M. i NAT. 

 size. Lateral view, d, Dia- 



POPHYSIS; S, GPINOUS PROCESS; 

 SK, SUTXTRE; 2, ANTERIOR ZY- 

 GAPOPHYSIS; z', POSTERIOR 

 ZYGAPOPIIYSIS. 



