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UNITED STATES NATIONAL MUSEUM BULLETIN 294 



Sixth dorsal.— The narrowing of the gap (85 mm.) 

 anteriorly between the prezygapopiiysial facets is con- 

 tinned on this dorsal. This dorsal has a slightly wider 

 neural spine (pi. 19, fig. 1) which rises at least 130 mm. 

 above the roof of the neural canal. The robust trans- 

 verse i)rocesses (diapophyses) are as wide as on the pre- 

 ceding dorsal, although slightly shorter and each 

 projects forward beyond the level of the anterior face 

 of the centrum. The rugose ovoidal facet on the extrem- 

 ity of each diapophysis (length, 47 mm.; vertical diam- 

 eter anteriorly, 26 mm.) for the tuberculum of the sixth 

 rib is concave horizontally and slopes obliquely down- 

 ward and inward from the dorsal to ventral margins. 

 The basal portion of each diapophysis arises from the 

 thickened pedicle (minimum transverse width, 32 mm.) 

 and from the dorsoexternal portion of the centrum an- 

 teriorly. The low blunt metapophyses project strongly 

 beyond the level of the anterior face of the centrum; 

 each is traversed anteroposteriorly by a rounded ridge 

 which delimits externally the prezygapopiiysial facet. 

 The narrow elongated prezygapopiiysial facets are 

 deeply concave from side to side. The postzygapophys- 

 ial facets are very narrow and project strongly back- 

 ward beyond the level of the posterior face of the cen- 

 trum. The contour of the anterior face of the centrum 

 ( pi. 20, fig. 6) is similar to that of the fifth, but the 

 median ventral longitudinal I'idge on the centrum is less 

 l)rominently developed, although the lateral surfaces 

 continue to be deeply excavated. The posteroexternal 

 facet for the capitulum of the seventh rib is quite pro- 

 tuberant and the anteroexternal demifacet persists. 



Seventh dorsal.— The vertical diameter (27 mm.) 

 of the neural canal anteriorly on this dorsal is less than 

 that of any other dorsal. An increase in the length 

 (81 mm.) of the centrum as well as in its width an- 

 teriorly (108 mm.) is not unusual in this portion of the 

 dorsal series. Thick pedicles (riglit, minimum trans- 

 verse diameter, 34 mm.) of the neural arch give origin 

 (<) the transverse processes (diapophyses) which pro- 

 ject outward horizontally and extend forward beyond 

 t lie level of the anterior face of the centrum. The rugose 

 facet on the extremity of each diapojihysis for the tuber- 

 culum of the seventh rib is elongated (length, .52 mm.; 

 vertical diameter medially, 24 mm.), shallowly concave 

 from end to end, and its articular face is more nearly 

 vertical. The low, flattened, anteriorly rounded and for- 

 ward projecting metapophyses are traveised antero- 

 posteriorly by a prominent crest which delimits 

 externally each prezygapophysial facet. P^ach prezy- 

 gapopiiysial facet is very narrow anteriorly but in- 

 creases in width and concaveness toward the base of the 

 neural spine. The postzygapophysial facets are very 



narrow and extend backward beyond the level of the 

 posterior face of the centrum. The neural spine (pi. 19, 

 fig. 2) is broader than that of the preceding dorsal and 

 rises 150 ± mm. above the roof of the neural canal. The 

 contour of the anterior face of the centrum (pi. 20, fig. 

 7) is similar to that of the sixth, but the median ventral 

 longitudinal ridge on the centra of the anterior dorsals 

 is not developed. The lateral surfaces of the centrum 

 are deeply excavated. The posteroexternal facet for the 

 capitulum of the eighth rib is situated mainly on the 

 posterior face of the prominent protuberance. The an- 

 teroexternal demifacet is larger than on the sixth. 



Eighth dorsal. — On this dorsal one observes the 

 accentuation of the previously developing anteropos- 

 terior crest which has now culminated in the shift of 

 each metapophysis from horizontal to vertical. This 

 development permits the pair of metapophyses to limit 

 the side to side movement of the postzygapophyses of 

 the preceding dorsal. Each broad transverse process 

 (diapophysis) projects outward from the transversely 

 widened (40 mm.) robust pedicle of the neural arch and 

 from the dorsoexternal portion of the centrum ante- 

 riorly and is bent upward, extending very slightly be- 

 j'ond the level of the anterior face of the centrum. The 

 rugose facet for the tuberculum of the eighth rib on the 

 extremity of each diapophysis is elongated (length, 54 

 mm.; vertical diameter anteriorly, 21 mm.), subcrescen- 

 tic in outline and deeply excavated medially. The back- 

 ward projecting postzygapophysial facets are quite 

 narrow and closely approximated. Tlie neural spine 

 (minimum width, 74 mm.) is broader (pl.l9.fig.3) than 

 that of the preceding dorsal, abruptly truncated at the 

 extremity, and rises 160 mm. above the roof of the neu- 

 ral canal. The contour and width of the anterior face (pi. 

 20, fig. 8) of the centrum are similar to the seventh dor- 

 sal. No vestige of the median ventral longitudinal ridge 

 is discei-nible on the centrum and the lateral surfaces 

 are even more strongly excavated. The posteroexternal 

 protuberance for articulation with the capitulum of the 

 ninth rib is reduced in size as contrasted with that of the 

 seventh, and the anteroexternal demifacet is similar 

 to that of the seventh dorsal. 



Ninth dorsal. — In contrast to those on the eighth 

 dorsal, the greatly enlarged metapophyses now rise 48 

 mm. above the floor of the neural canal, and the gap 

 between them is 54 mm. Each metapophysis is com- 

 pressed from side to side, obtusely pointed anterodor- 

 sally, extended forward beyond the level of the anterior 

 face of the centrum, and contributes the outer wall of 

 the rather narrow prezygapophysial facet. On the first 

 to eightli dorsals, inclusive, the transverse process 

 (diapophysis) projects outward mainly from the more 



