CETOTHERES FROM THE MIOCENE CHOPTANK FORMATION 



37 



The rather thick pedicles of the neural arch (length, 

 67 mm.) support transversely thickened metapophyses 

 (length doi"soexternal edge of right, T4 mm.) which 

 are strongly upturned distally and rise 50 mm. above 

 the dorsal rim of anterior epiphysis; the distance be- 

 tween the dorsoextenial edges is 102 mm. 



The neural spine (pi. 23, fig. 4) is broader (84 mm.) 

 but shorter than that of the third caudal, and rises 70 

 mm. above the roof of the neural canal. 



Fifth caudal. — Ventrally on each side of the cen- 

 trum, the anterior and posterior liaemal tubercles are 

 united by a continuous osseous strip which borders com- 

 pletely the open groove or channel for the caudal 

 artery, an ascending branch of which emerges laterally 

 through a rather large orifice (width, 19 mm.) and con- 

 tinues upward on the external face of the centrum in 

 front of the anterior notch at the base of the transverse 

 process. The lateral surfaces (pi. 23, fig. 5), both above 

 and below the transverse processes, are deeply hollowed 

 out; both ends of the centrum are slightly convex. The 

 transverse processes (pi. 24, fig. 5) are short, obliquely 

 truncated distally, the anterior angle projecting out- 

 ward farther than the posterior angle. The thick 

 metapophyses (length right, 62 imn.) are directed 

 upward and outward, but cannot clasp the posterior 

 median angle of the neural arch of the preceding 

 caudal. These metapophyses rise 44 mm. above the 

 dorsal rim of the anterior epiphysis; the distance 

 between the dorsoexternal edges is 92 mm. The thick 

 pedicle (length, 66 mm.) of the neural arch is approxi- 

 mately the same length as that of the fourth caudal. 

 The thin neural spine is vestigial, reduced to a thin 

 longitudinal ridge, and the neural canal small (pi. 25, 

 fig. 5). 



Sixth cattdal. — Ventrally on each side the anterior 

 and posterior haemal tubercles are united by a some- 

 what thickened osseous connection and as on the Y>re- 

 ceding caudal a branch of the caudal artery emerges 

 laterally through a large foramen. On its upward 

 course, however, this arterial branch passes through the 

 perforation in the greatly shortened transverse proce^ss 

 (pi. 23, fig. 6). The lateral surfaces of the centrum are 

 deeply hollowed out above and below the transverse 

 process; the anterior end of the centrum is flattened and 

 the posterior end is slightly convex. The transverse 

 processes (pi. 24, fig. 6) are very short-, obliquely trun- 

 cated distally and perforated at the base. Each thick- 

 ened pedicle of the neural arch is low, and the trans- 

 verse diameter of the neural canal (pi. 25, fig. 5) 

 exceeds the vertical. The left j^edicle is perforated near 

 the posterior end of the roof of the neural arch. The 



thick metapophyses (length, 48 mm.) rise 31 mm. above 

 the dorsal rim of the anterior epiphysis; the distance 

 between the dorsoexternal edges is 75 mm. The thin and 

 very low neural spine extends irregularly the length of 

 the roof of the neural arch. 



Seventh caudal. — On each side the transversely 

 widened anterior and posterior haemal tubercles are 

 united by a much thicker osseous connection (pi. 23, 

 fig. 7), each of which is perforated medially to permit 

 the passage of a branch of the caudal artery which on 

 its upward course passes through a foramen in the 

 base of the ridge-like thickened transverse process. The 

 ventral open groove or channel for the caudal artery is 

 deep. The lateral surfaces of the centriun above and 

 below the transverse processes are hollowed out; both 

 ends of the centrum are more flattened than convex. 

 Each low pedicle of the neural arch extends most of 

 the length of the dorsal surface of the centnmi, and is 

 pierced medially at the base by a small foramen. The 

 oval neural canal (pi. 25, fig. 7) is very small and the 

 neural spine is low. The markedly reduced oval knob- 

 like metapophyses (length, 36 mm.) rise 29 mm. above 

 the dorsal rim of the anterior epiphysis: the distance 

 between the dorsoexternal edges is 59 mm. 



Eighth caudal. — This caudal resembles the seventh 

 in having the anterior and j^osterior haemal tubercles 

 (pi. 23, fig. 8) united by a thick osseous connection, per- 

 forated medially for the passage of a branch of the 

 caudal artery. This vascular branch likewise continues 

 its upward course through the perforation in the very 

 low and thick basal remnant of the transverse process. 

 The lateral surfaces of the centrum are less noticeably 

 hollowed out; the posterior end of the centrum is 

 slightly more convex than the anterior end. The 

 metapophyses (pi. 25, fig. 8) are reduced to small, low, 

 oval knobs. A low, thin neural spine (length, 36 mm.) 

 persists on the short (length, 42 mm.) roof of the 

 neural arch. The roof of the neural arch completely 

 encloses the small neural canal, no larger than the diam- 

 eter of a pencil. 



Ninth caudal. — The anterior end (pi. 25, fig. 9) of 

 this caudal is higher than wide ; the lateral surfaces of 

 the centrum are much less hollowed out, and the poste- 

 rior end is slightly convex and the anterior end is flat- 

 tened. A tendency exists for the posterior end of these 

 terminal caudals to become smaller than the anterior 

 end as well as more convex. Tlie centrum is pierced 

 dorsoventrally by a large vascular aqueduct on each 

 side external to the low, thickened pedicle of the neural 

 arch; their closely approximated ventral orifices are 

 located in a deep elongated haemal groove or channel. 



