14 



UNITED STATES NATIONAL MUSEUM BULLETIN 294 



the second rib slopes obliquely downward and inward 

 from dorsjil to ventral margin. The stronj; pedicles of 

 the neural arcli are broad (right, niininuiin transverse 

 diameter, 41 mm.) and very short; they support the 

 roof of the neural canal as well as contributing a por- 

 tion of the base of the diapophysis. Tiie small ovoidal 

 prezygapophysial facets are limited externally by a low 

 ridge. The jiostzygapopliysial facets are elongated, 

 nuich larger, and slope obliquely downward from 

 external to internal nuirgins. The distally attenuated 

 neural spine (pi. 8, fig. 1) rises 54 mm. above the roof 

 of tiic neural canal. The doi-soventraliy elongated hemi- 

 circular and protuberant facet on the posteroexternal 

 angle of the centnun for the head of the third rib seem- 

 ingly does not share this function with a similar oppos- 

 ing surface on the anteroexternal angle of the centrum 

 of the third dorsal. Viewed from in front the centrum 

 is uniformly elliptical. 



Third dors.vl. — A decrease in the length (98 mm.) of 

 the diapophysis, a shift in the direction of the main axis 

 of tlie terminal facet for tiie tuberculum of the third rib 

 from dorsoventral to anteroposterior and an increase in 

 the thickness of the centnun characterize this vertebra 

 (USNM 23794). Very little if any alteration in the 

 dimensions of the neural canal are observable. Each 

 broad diapophysis (pi. 7, fig. 2) projects outward but 

 more strongly forward than on the preceding dorsal. 

 The wide pedicles (36 mm.) of the neural arch support 

 the low roof of the neural canal as well as contributing 

 a portion of the base of the diapophysis. An external 

 sharp-edged ridge limits externally the elongated 

 (length, 60 nmi.) shallowly concave prezygapophysial 

 facet. Both postzygapophysial facets are pitted and 

 partially deformed by osteophytosis. The short, distally 

 attenuated neural spine (pi. 8, fig. 2) rises 62 mm. above 

 the roof of the neural canal. The posteroexternal hemi- 

 circular facet for the capitulum of the fourth rib is 

 smaller than, but is as protuberant as, the corresponding 

 facet on the preceding dorsal. Viewed from in front the 

 centrum (pi. 6, fig. 2) is elliptical, dorsoventrally com- 

 pressed. A dorsoventrally compressed bony process 

 projects backward for 20 mm. from the ventroexternal 

 border of the centnim on the left side. 



Fourth dorsal. — Each broad (minimum width, 55 

 mm.) dorsoventrally compressed diapophysis (pi. 6, fig. 

 3) projects outward from the short stout pedicle of the 

 neural arch and extends forward beyond the anterior 

 face of the centrum. The extremity of the diapophysis 

 is horizontally widened to provide an elongated facet 

 (40 mm.) for the tuberculum of the fourtli i-ib. Each 

 elongate and concave prezygapophysial facet (pi. 7, 

 fig. 3) slopes obliquely downward from the external 



sharp-edged ridge or crest to its inner thin edge. The 

 distance between these external ridges anteriorly is 110 

 mm. The narrow elongate postzygapophysial facets 

 slope obliquely downward from external to internal 

 margins. The low roof of the neural canal is almost 

 horizontal. No material change in either the transverse 

 or vertical diameter of the neural canal is observable. 

 The short distally rounded neural spine (pi. 8, fig. 3) 

 rises 67 mm. above the roof of the neural canal. The 

 protuberant posterior hemicircular facet for the capitu- 

 lum of the fifth rib is larger than that of the preceding 

 dorsal. Viewed from in front the profile of the centrum 

 (USNM 23794) is more quadrangular than elliptical. 

 Ventrally the rims of the anterior and posterior 

 epiphyses are extruded and irregular. 



Fifth dorsal. — An increase in the minimum antero- 

 po.sterior diameter (37 mm.) of the right pedicle of the 

 neural arch, a reduction in the transverse diameter ( 72 

 mm.) of the neural canal (pi. 6, fig. 4), but no appreci- 

 able reduction of the distance (109 mm.) between the 

 external crest-like margins of the opposite prezygapo- 

 physial facets anteriorly characterize this dorsal 

 (USNM 23794). Both dorsoventrally compressed dia- 

 pophyses (pi. 7, fig. 4) are a little broader (minimum 

 width, 57 mm.) but shorter than those of the preceding 

 dorsal ; they project outward and extend forward well 

 beyond the level of the anterior face of the centrum and 

 have a more elongated (length, 45 mm.) ovoidal concave 

 tubercular facet at the extremity. Prezygapophysial 

 and postzygapophysial facets are similar to those of the 

 preceding dorsal. The distally truncated neural spine 

 (pi. 8, fig. 4) has increased in width and rises 82 mm. 

 above the roof of the nueral canal. No increase or de- 

 crease in the size of the hemicircular protuberant pos- 

 teroexternal facets for the capitulum of the following 

 rib is observable. Doreoventrally compressed bony ex- 

 crescences project backward from the posteroventral 

 edge of the centrum on each side. 



Sixth dorsal.— This dorsal (USNM 23794) has a 

 large bony excrescence (pi. 8, fig. 5) projecting back- 

 ward from the ventral border of the centrum on the 

 right side which certainly limited freetlom of move- 

 ment of this vertebra. A less noticeable decrease in the 

 transverse and vertical diameters of the centrum and of 

 the neural canal (pi. 6, fig. 5) has occurred. The distance 

 between the outer margins of the deeply concave prezyg- 

 apophysial facets has been reduced to 95 mm. and the 

 postzygagophysial facets have become somewhat nar- 

 rower. The diapophyses (pi. 7, fig. 5) have been slightly 

 shortened, but are extended forward beyond the level 

 of the anterior face of the centrum ; the terminal con- 

 cave facet of the diapophysis for the capitulum of the 



