CETOTHERES FROM THE MIOCENE CHOPTANK FORMATION 



35 



face of the centrum. Neither pro- nor post-zygapophys- 

 ial facets are present. The vertical diameter (27 mm.) of 

 the neural canal (pi. 22, fig. 5) anteriorly exceeds its 

 transverse diameter (21 mm.) . 



The centra of the last two lumbars are larger and 

 longer than that of the first lumbar which appears to 

 be normal for these Miocene cetotheres. The length of 

 this lumbar is 136 mm. The contour of the anterior end 

 of the centrum tends to approach that of the first 

 caudal, including an increase in the transverse (115 

 mm.) and vertical (105 mm.) diameters. A low ven- 

 tral longitudinal keel is present between the concave 

 depressions on the ventral surface. 



Twelfth ltjmbar. — The dimensions of the centrum 

 have increased very slightly over those of the eleventh. 

 The metapophyses, however, are more noticeably 

 obliquely inclined upward and outward, the neural spine 

 is shorter, and the width of the transverse process is in- 

 creased. These broad transverse processes (pi. 22, fig. 4) 

 project outward, slightly downward and ai-e inclined 

 a little forward. 



The width of the neural spine (pi. 22, fig. 2) has de- 

 creased; it rises 153 mm. above the roof of the neural 

 canal and the backward projecting dorsal portion of the 

 neural arch continues to extend beyond the level of the 

 posterior face of the centrum. The length (69 mm.) of 

 the thin pedicle of the neural arch exceeds that (67 

 mm.) of the pedicle of the eleventh lumbar. These 

 pedicles support rather long (lengtli, 76 mm. at dorsal 

 edge) metapophyses which are more noticeably spread 

 apart (distance between dorsoexternal edges, 72 mm.) 

 than on preceding lumbar, project forward beyond 

 level of anterior face of centrum, and rise 61 mm. above 

 the dorsal rim of the anterior epiphyses. Neither pre- 

 nor postzygapophysial facets are present. The vertical 

 diameter (27 mm.) of the neural canal (pi. 22, fig. 6) 

 anteriorly exceeds its transverse diameter (19 mm.). 



The end profiles of the centrum are not subcordate; 

 the dimensions of the posterior end are approximately 

 the same as those of the anterior end of the first caudal. 

 A prominent longitudinal keel separates the opposite 

 portions of the central surface of the centrum. 



CAUDAL VERTEBRAE 



All twelve of these caudal vertebrae (USNM 23636) 

 have the epiphyses firmly ankylosed to the centra. In 

 so far as our present knowledge goes, it would appear 

 that two and possibly three of the terminal caudals 

 are not represented in this series. Sixteen caudal verte- 

 brae were present in the skeleton of the middle Miocene 

 (Helvetian) Mesocettn^ hungancun (Kadic, 1907, p. 75). 



At least one (USNM 16667) of the Calvert cetotheres 

 possessed 14 caudals. The centrum of the first caudal 

 is slightly longer than the twelfth lumbar behind the 

 first the centra progressively decrease in length toward 

 the terminal end of this series. The interval between the 

 dorsal edges of the opposite metapophyses progres- 

 sively diraiiaishes behind the third caudal. Behind the 

 second caudal the height of the neural spine rapidly di- 

 minishes. The shortening of the transverse process ter- 

 minates in the short flange-like condition present on the 

 sixth caudal. 



On the first caudal a pair of ventral posterior haemal 

 tubercles (haemapophyses) replace the ventral keel of 

 the lumbar vertebrae and constitute the lateral limits 

 of the haemal groove which on succeeding caudals be- 

 comes more excavated with the increased development 

 of these paired tubercles. The anterior pair of haemal 

 tubercles are ill defined and weakly developed on the 

 three anterior caudals; the posterior pair of haemal 

 tubercles increase in size from the first to the third 

 caudal. On the fifth, sixth, seventh, and eighth caudals 

 on each side of the longitudinal haemal groove, the an- 

 terior and posterior haemal tubercle are united by a 

 continuous osseous connection through which the vas- 

 cular branches emerge laterally in a medially located 

 orifice. These segmental blood vessels pass through a 

 perforation at the base of the transverse process on each 

 side on their upward course. Behind this caudal the 

 centra of the terminal caudals are pierced dorsoven- 

 trally on each side by a vertical aqueduct for the passage 

 of these segmental blood vessels. 



Including a 4 mm. allowance for the cartilaginous 

 intervertebral disks, this consecutive series of twelve 

 caudals and two additional terminal caudals provide a 

 fairly accurate estimated length of 1370 mm. (54 inches) 

 for the tail. See table 22 for measurements of the caudal 

 vertebrae. 



First cattdal. — The neural spine of the first caudal 

 is considerably shorter than that of the posteriormost 

 lumbar rising 142 mm. above the dorsal rim of anterior 

 epiphysis and the length of the centrum is slightly 

 greater. The centrum (pi. 23, fig. 1) is deeply hollowed 

 out laterally, both above and below the transverse proc- 

 esses. Haemal tubercles (haemapophyses) separated by 

 a broad longitudinal open groove or channel are de- 

 veloixid at the posterior end of the ventral surface of 

 the centrum for articulation with the chevron bone. 

 The anterior haemal tubercles are rudimentary, if pres- 

 ent. Relatively minor widening (125 mm.) modifies the 

 circular contour of the posterior end of the centrum. 

 Both ends are somewhat flattened. The transverse proc- 

 esses (pi. 24, fig. 1) are broad (minimum anteroposteri- 



