CETOTHERES FROM THE MIOCENE CHOPTANK FORMATION 



13 



transversely widened lower process (parapopliysis) to 

 enclose the large cervical extension of the thoracic retia 

 mirabilia. This parapophysis is dorso vent rally com- 

 pressed toward its base. 



Fourth cervical. — All lateral processes as well as the 

 pedicles of the neural arch are broken off near the 

 base on this cei-vical (USNM 23794). The anteropos- 

 teriorly compi-essed upper transverse process (di- 

 apophysis) projected outward from the pedicle of the 

 neural arch; the parapophysis projected outward and 

 downward. The anterior face of the centrum is more 

 flattened than convex in contrast, to the concave pos- 

 terior face. 



Fifth cervical. — Except for a noticeable increase 

 in the width of the neural canal, tliis cervical (USNM 

 23794) does not differ materially from the preceding. 



Sixth cervical. — Minor alterations including a grad- 

 ual decrease in the aiiteroposterior diameter of the 

 p>edicle of the neural arch, an increase in the transverse 

 diameter of the neural canal, and tlie vertical diameter 

 of the centrum are observable from the third to the sixth 

 cervical (USNM 23794). Upper as well as lower trans- 

 verse processes were present. 



DORSAL VERTEBRAE 



All twelve dorsal vertebrae (USNM 23794) were found 

 at the time of excavation in their original undisturbed 

 sequence, although only the neural arch and neural 

 spine of tiie first dorsal was found. The centrum of tliis 

 dorsal and its diapophyses had previously been broken 

 off and removed by some visitor at the site. Both 

 epiphyses are firmly ankylosed to the centrum of each 

 of these eleven dorsals. Spondylitis deformans or osteo- 



phytosis presumably limited the movement but did not 

 bind together the third to tenth dorsals, inclusive, 

 which have bony outgrowths protruding posteriorly on 

 one or both sides from the ventral border of the 

 centrum. 



On each side of the centnim of the second to seventh 

 dorsals, inclu.sive, the facet for the head of the follow- 

 ing rib is located obliquely on a well-defined posterior 

 tuberosity below the level of the floor oi the neural canal 

 on the second but gradually becomes located higlier on 

 the lateral surface. 



The pedicles of the neural arch on the seven anterior 

 dorsals are very low and broader transversely than 

 anteroposteriorly. Shortening of the pedicles and flat- 

 tening of the roof of the neural canal had produced an 

 unusually low neural canal, the vertical diameter 

 anteriorly being equivalent to less tiian one third (sec- 

 ond, 78X27 mm.) to one fourth (sixth, 70X17 mm.) 

 of the transverse diameter. A median longitudinal ridge 

 on the floor of the neural canal increases in prominence 

 behind the seventh dorsal. The total length of the twelve 

 dorsals, including the cartilaginous intervertebral 

 disks, is about 960 mm. (373^ inches). See table 12 for 

 additional measurements of the dorsal vertebrae. 



First dorsal. — The neural spine of this dorsal 

 (USNM 23794) was short, rising 35 mm. above tiie roof 

 of the broad neural canal, and truncated obliquely from 

 its anterobasal edge to its posterodorsal apex. 



Second dorsal. — Except for the left diapophysis this 

 dorsal (USNM 23794; pi. 6, fig. 1) is complete and 

 shows no indication of osteophytosis. The stout right 

 diapophysis (length, 115 mm., pi. 7, fig. 1) projects out- 

 ward, slightly downward and somewhat forward; the 

 large, triangular terminal facet for the tuberculum of 



