CETOTHERES FROM THE MIOCEI^fE CHOPTANK FORMATION 



29 



The distal ends of the thicker parapophyses are curved 

 upward and backward. 



Fifth cervical. — As contrasted with the fourth cer- 

 vical, the vertical diameter of the anterior face of the 

 centrum has increased, the neural canal is wider, and 

 the oijening for the cervical extension (pi. 17, fig. 6) of 

 the thoracic retia mirabilia is less completely closed. The 

 pedicles (right, minimum transverse diameter, 38 mm.) 

 of the neural arch are short, but occupy more of the 

 dorsoexternal face of the centrum. Each pedicle supports 

 a wide (right, maximum width, 2.3 m.) concave prezy- 

 gapophysial facet, which projects forward beyond the 

 level of the anterior face of the centrum. The postzyga- 

 pophysial facets are also wide and slope obliquely down- 

 ward from external to internal margins. A short neural 

 spine (pi. 18, fig. 5) rises from the top of the neural 

 arch. The slender diapophyses which project outward, 

 but curve downward and backward, arise partly from 

 the pedicle of the neural arch and partly from the dorso- 

 external portion of the centrum anteriorly. The left di- 

 apophysis is longer than the right. Each short para- 

 pophysis or lower transverse process projects outward 

 and curves upward and backward ; the increase in width 

 is gradual on the basal two-thii'ds of its length, but the 

 distal end is attenuated. The extremities of the upper 

 and lower transverse processes are separated by a gap, 

 and thus do not completely enclose the foramen trans- 

 versarium. The ventral surface of the centrum is de- 

 pressed on each side of the low longitudinal median 

 ridge. 



Sixth cervical. — The contour of the anterior face 

 of the centrum (pi. 17, fig. 8) has become more nearly 

 subcordate and the transverse diameter continues to ex- 

 ceed the vertical. The pedicles (right, minimum trans- 

 verse diameter, 40 mm.) of the neural arch are short and 

 wide but the major support to each diapophysis is con- 

 tributed by the dorsoexternal portion of the centrum 

 anteriorly. Each pedicle supports an elongate concave 

 prezygapophysial facet which projects forward beyond 

 the level of the anterior face of the centrum. The post- 

 zygapophysial facets are ovoidal but slope less notice- 

 ably downward from external to internal margins; they 

 project backward beyond the level of the posterior face 

 of the centrum. The neural spine (pi. 18, fig. 6) is short. 

 The dimensions of the neural canal do not differ ma- 

 terially from those of the fifth cervical. Each slender 

 diapophysis projects outward and curves downward and 

 backward to its attenuated extremity. No vestige of the 

 parapophysis or lower transverse process persists. On 

 each side of the low median longitudinal ridge the con- 

 cavely depressed ventral surface merges with the simi- 

 larly depressed lateral face. 



Seventh cervical. — The anterior face of the centrum 

 (pi. 17, fig. 9) is subcordate. The median longitudinal 

 ridge on the ventral face of the centrum is much nar- 

 rower and more prominent than the corresponding broad 

 ridge on the preceding cervical. The pedicles of the 

 neural arch are low and support the forward projecting 

 elongated concave prezygapophysial facets which are 

 not symmetrical. The inward slanting postzygapophys- 

 ial facets are elongated. The neural spine (pi. 18, fig. 7) 

 is slender, triangular in outline, with subacuminate 

 apex. The diapophyses are dorsoventrally widened at 

 the base and project outward from the dorsoexternal 

 portion of the centrum anteriorly. Each diapophysis 

 terminates distally in an elongated facet (40 x 15 mm.) 

 for articulation with the head of the anterior or cervical 

 limb of the bifurcated first rib. Each diapophysis is 

 compressed in an anteroposterior direction and slopes 

 obliquely downward from upper to lower margin. No 

 vestige of the ventral transverse process is present. 



DORSAL VERTEBRAE 



All of the epiphyses on the cervical, dorsal, lumbar, and 

 caudal vertebrae associated with these skeletal remains 

 were firmly ankylosed to their respective centra, an indi- 

 cation of physical maturity. All of the dorsal vertebrae 

 were found during excavation in their original undis- 

 turbed sequence. The centra increase in length from the 

 first to the twelfth and on all the transverse diameter 

 exceeds the vertical diameter of the anterior end. The 

 profiles of both ends of consecutive dorsal centra are 

 modified from a transvei-sely widened subcordate ante- 

 riorly to a less noticeably dorsoventrally compressed 

 subcordate posteriorly. On each side of the centrum of 

 the first to eighth dorsals inclusive, below the level of the 

 floor of the neural canal and adjacent externally to or 

 on the edge of the posterior epiphysis of the centrum, 

 there is an articular facet for reception of the capitulum 

 of the following rib. On the anterior border of the next 

 following centrum adjacent to this posteroexternal facet 

 a narrower articular surface is formed for the hinder 

 border of the head of tlie same rib. 



The neural canal decreases in width from the first to 

 twelfth dorsals. On the anterior eight dorsals the ped- 

 icles of the neural arch are massive and wide. The 

 diapophyses progressively increase in width on the eight 

 anterior dorsals and, on all, these processes arise in part 

 from the pedicle of the neural arch and in part from 

 the dorsoexternal portion of the centrum anteriorly. The 

 parapophyses of the ninth to twelfth dorsals, inclusive, 

 project outward from the lateral surface of the centrum. 

 The neural spines increase in height from the first to 



