98 BULLETIN 110, UNITED STATES NATIONAL MUSEUM. 



The pubic and ischiac peduncles of the attached ilia coincide with Si and S 3 , 

 respectively, as they do in Antrodemus , Tyrannosaurus , and Gorgosaurus. 



Only the spinous processes of the two posterior sacrals are preserved intact 

 (see pi. 30); but from the fact that they are fused throughout their length it is 

 inferred that all were probably fused to form a continuous plate, the upper end of 

 which extended somewhat above the superior borders of the ilia, and it has so 

 been restored in the mounted skeleton. Whether this plate was perforated by 

 fenestrations, as in Tyrannosaurus, 1 remains yet to be determined. 



The greatest length of the coalesced sacral vertebrae is 380 mm. 



Measurements of sacral vertebrae of Ceratosaurus nasicornis Marsh. 



Length of centrum: rnm. 



8 r 84 



S, 73 



S 3 71 



S 4 72 



S 6 80 



Greatest height over all: 



At center of S 4 291 



At center of S 5 284 



Caudal vertebrae. — There are 50 caudal vertebrae present in the type specimen. 

 In the mounted skeleton (see pi. 30) there are 51 vertebrae, the twenty-seventh 

 being entirely restored. There is at least one vertebra missing from the distal 

 end of the tail, and in all probability two or more, so that in the complete caudal 

 series of Ceratosaurus there would be at least 53 vertebrae. 



The first 16 anterior caudal vertebrae were found articulated with the sacrum. 

 The seventeenth to the twenty-sixth, inclusive, formed a second articulated series, 

 and though no contact could be found connecting this series with the one anterior 

 to it, the structure and relative size of these vertebrae was such as to indicate that 

 none were lacking between. In the original quarry map the collector indicated 

 two slightly displaced vertebrae between the second and third series. Only one 

 of these (the twenty-eighth in the mounted skeleton) was located in the collec- 

 tions, and it was largely on this evidence that the restored vertebrae (the twenty- 

 seventh) was introduced to take the place of the missing one. The twenty- 

 ninth to the fifty-first, inclusive, formed the third and final series and are shown 

 in the mounted skeleton (pi. 30), as found articulated. 



The tail is more than one-half the total length of the animal, measuring 9 feet 

 6 inches along the vertebrae, whereas the anterior half is 8 feet 10 inches to the 

 tip of the nose. It must have served as an efficient organ for maintaining the creature's 

 balance during locomotion. Although all of the caudals have interlocking zyga- 

 pophyses, even down to the extremely small ones near the tip, the tail was capable, 

 I think, of considerable flexion, as is indicated by the original and apparently 

 natural curves which are retained in the mounted skeleton. 



The caudal vertebrae are slightly procoelous relatively slender and light in 

 their construction, especially when compared with those of such forms as Antro- 

 demus, Gorgosaurus, and Tyrannosaurus. The centra of the anterior vertebrae are 



i Osborn, H. F. Bull. Amer. Mus. Nat. Hist., vol. 22, 1906, p. 289, text fig. 5. 



