30 



UNITED STATES NATIONAL MUSEUM BULLETIN 294 



the twelfth dorsals. The width of the gap between the 

 prezygapophysial facets decreases from the anterior to 

 the posterior end of the dorsal series. 



Oil the first to seventh dorsal vertebrae, the articular 

 facet on each metapophysis is horizontal and flat, al- 

 though an anteroposterior crest delimiting the outer 

 edge of the prezygapophysial facet progressively in- 

 creases in prominence. On the eighth dorsal this crestlike 

 development culminates in the shift in the inclination of 

 each metapophysis from horizontal to vertical. From 

 this dorsal vertebra to the hinder end of the lumbar 

 series these side to side compressed metapophyses pro- 

 gressively increase in size and rise higher above the level 

 of the floor of the neural canal. 



The total length of the consecutive series of twelve 

 dorsal vertebrae, including tlie cai-tilaginous interverte- 

 bral disks, did not exceed 101,5 mm. (40 inches). See 

 table 20 for measurements of the dorsal vertebrae. 



First dorsal. — In dimensions the centrum of the first 

 dorsal is not materially unlike the seventh cervical. The 

 tip of tlie subtriangular neural spine (pi. 18, fig. 8) rises 

 53 mm. above the roof of the neural canal; the Avidtli 

 (47 mm.) of this canal exceeds its height (35 mm.). The 

 short pedicles of the neural arch support the prezygap- 

 ophysial facets, which are elongated and extended for- 

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

 trum. A gap of 65±mm. separates the prezygapophysial 

 facets anteriorly. The postzygapophysial facets are 

 large and are concavely curved from side to side. The 

 diapophyses (pi. 20, fig. 1) are dorsoventrally widened. 



concavely depressed on anterior face and convex on 

 posterior face, and slope obliquely backward from up- 

 per to lower edge. Each diapophysis, which projects 

 outward and sliglitly forward, arises in part from the 

 pedicle (right, minimum transveree diameter, 49 mm.) 

 of the neural arcli and in part from the dorsoexternal 

 portion of the centrum anteriorly. The distal end of 

 each process is expanded dorsoventrally (vertical, 39 X 

 trans\erse, 12 mm.) to form the elongated facet for 

 articulation with the tuberculum of the posterior limb 

 of the bifid first rib. A large half-moon-shaped and 

 deeply concave facet with mai-kedly ele\'ated margins 

 for recejjtion of the capitulum of the second rib is located 

 on the posteroexternal angle of the centrum. On each 

 side of the rather broad median longitudinal ridge the 

 concavely depressed ventral surface of the centnnn 

 merges with tlie similarly depressed lateral face. 



Second dors.\l. — The base of the rather broad di- 

 apophysis (pi. 20, fig. 2) arises in j^art from the pedicle 

 of the neural arch and in part from the dorsoexternal 

 angle of the centrum anteriorly, and projects outward 

 and slightly forward. In cross-section this upper trans- 

 verse process is compressed in a dorso ventral direction 

 and the obliquely directed ovoidal facet (length, 42X25 

 mm. ) on its extremity for reception of the tuberculum 

 of the second rib is roughened by the presence of many 

 irregularly spaced pits, presumably for attachment of 

 a cartilaginous connection. The pedicles of the neural 

 arch are low and broad ; the minimum transverse diam- 

 eter of the right pedicle is 45 mm. The tip of the at- 



Table 20. — Measurements (in mm.) of the dorsal vertebrae, USNM SS6S6 



' Including posterior capitular facet. 



