38 



UNITED STATES NATIONAL MUSEUM BULLETIN 294 



No vestige of either transverse process persists. The roof 

 of the very small neural arch, although short (27 mm.), 

 is complete, and the low lateral pedicles are broad. A 

 small foramen at the base of the right pedicle (pi. 23, 

 fig. 9) about halfway of its length provides a vascular 

 pivssage to the neural canal from the lateral vertical 

 aqueduct. 



Tenth OAtroAL. — This vertebra is characterized by the 

 marked foreshortening (pi. 23, fig. 10) of the centrum 

 (length, 57 mm.) and the reduction of the lateral ridges 

 bounding the ventral haemal channel for the caudal 

 artery. A very short bone isthmus (length, 5 mm.) 

 bridges the very narrow neural canal. Tlie centrum is 

 l)ierced dorsoventrally by two vascular aqueducts, the 

 two large orifices of which are located in an oval de- 

 prassion on the ventral face of the centrum. Dorsally, 

 each of these aqueducts has two or more orifices located 

 on each side of the narrow partially roofed-over neural 

 canal. The anterior end of (i)l. 2.5, fig. 10) of the cen- 

 trum is flattened and the posterior end is convex. The 

 dorsal and ventral surfaces of this caudal have deep 

 scratches made by shark teeth. 



Eleventh cattdal. — The anteinor end (pi. 25, fig. 11) 

 of the centrum althougli depressed medially is some- 

 what flattened, and the posterior end is convex. The cen- 

 trum of this caudal is .smaller and shorter (pi. 23, fig. 

 11) than that of the tenth and no remnant persists of 

 the neural arch. The vertical vascular aqueducts that 

 pierce the centrum medially have two dorsal orifices 

 and three ventral orifices. The pair of vertical vascular 

 aqueducts, separated by a 14 mm. interval, open dor- 

 sally into a shallow oval cavity. Ventrally a wider in- 

 terval (31 mm.) separates the two largest orifices and 

 about halfway between them is a much smaller orifice. 



Tlie ventral and dorsal surfaces are deeply incised 

 or scratched by shark teeth. 



T^vELF^H CAUDAL. — The .smallest of these terminal 

 caudals also has the anterior end of the centrum (pi. 

 23, fig. 12) strongly depressed medially and the posterior 

 end convex. On the flattened dorsal face of the centrum 

 two orifices of the vertical vascular aqueducts are sepa- 

 rated by an interval of 10 mm. and ventrally by an in- 

 terval of 23 mm. Viewed from in front the outline of 

 this caudal is quadrangular: its lateral surfaces being 

 grooved longitudinally about the middle of their height. 

 The posterior and ventral surfaces are deeply incised 

 and mutilated by shark teeth; pieces have been bitt-en 

 out of the right and dorsal sides of the vertebra. A split 

 tooth of a tiger shark {Galeocerdo) is embedded in the 

 gashed dorsal surface of this caudal. 



CHEVRONS 



Six chevron bones (USNM 23636) were excavated 

 beneath the consecutive caudal vertebrae, seemingly at 

 their normal lo(;ation. The largest chevron lay beneath 

 the fourth caudal and the smallest, apparently the ter- 

 minal chevron, below the ninth caudal. 



Inferentially one or two anterior chevrons may have 

 exceeded the size of the chevron found beneath the 

 fourth caudal. Anterior to the origin of the horizontal 

 caudal flukes, the chevrons are attached on the skeletons 

 of Recent mysticetes below the intervertebral space be- 

 tween two caudals. Assuming a similar method of at- 

 tachment on this cetothere skeleton, not more than nine 

 chevrons were present. Five of these chevrons have a 

 definite haemal spine, whose anteroposterior diameter 

 decreased toward the last one. All six chevrons have a 

 "Y" profile when viewed from in front and have large 

 articular facets on the horizontally widened dorsal ends 

 of the lateral lamina. The minimum interval between 

 these articular facets is decreased almost imperceptibly 

 between the fourth and the seventh chevrons and al- 

 though in the same direction the trans^-erse diameter is 

 diminished, no obvious shortening is observable in the 

 length of the articular surface. The haemal canal of 

 these chevrons is smooth without trace of a median ven- 

 tral ridge, but it decreases in diameter toward the ter- 

 minal chevron. See table 23 for measurements of the 

 chevrons. 



Table 23. — Measurements (in mm.) of chevron hones, USNM 



23636 



Vertical diameter of chevron 



Greatest anteroposterior diam- 

 eter of haemal spine at ex- 

 tremity 



Anteroposterior diameter of 

 combined articular facets on 

 base of right lateral lamina 



Least distance between internal 

 margins of articular facets 



4(fe 5th 6th 7th Sth 9th 

 108 78 73 61 40 29 



92+ 106 91 84 66- 43 



57 60 63 .58 ,52 31 



13 9 11 11 7 7 



Fourth chemion. — This chevron (pi. 20, fig. 9) is the 

 largest of the six, but lacks the posterior end of the 

 haemal spine, whose vertical diameter (70 mm.) exceeds 

 the othei-s. The bluntly pointed anterior projection prob- 

 ably was shorter than the more slender posterior end. 

 The ovoidal transversely widened (28 mm.) articular 

 facets are large (length, 57 mm.) attenuated anteriorly 

 and rounded posteriorly. 



