THE VERTEBRAL COLUMN. 



47 



concretion in which they were embedded are so weathered that it is not possible to determine with 

 certainty all the characters of this region, though it can be stated with considerable certainty that 

 there were not more than 21 vertebrae [22] in the presacral series. The number of caudals is 

 entirely conjectural, since in no skeleton jet found is this region sufficiently complete to make 

 possible even a fairly probable estimate of the number of caudals. The number of cervicals is 



Fig. 4S. — Presacral vertebral series of type of Triceratops brericornus, No. 1S34, Yale Museum 



placed at 7 [S], and the division between the cervical and dorsal series is indicated not so much by 

 differences in the vertebras themselves as by the differences in the ribs which they support. These 

 were fortunately in position in this region of the vertebral column in the type of Triceratops 

 brevicornus, and the rib of the eighth [ninth] vertebra is unquestionably a thoracic rib with a 

 strong lateral curve and differing greatty from the straight cervical ribs of the sixth [seventh] and 

 seventh [eighth] cervicals. Between the last cervical and the first dorsal vertebra? the change is 

 great, though far less marked than between the second and third dorsals, and were it not for the 

 presence of the ribs, which in all herbivorous dinosaurs offer a more certain guide for distinguish- 

 ing between the vertebras of these two regions, one might very naturally be brought to the errone- 

 ous conclusion that the division between the cervical and dorsal series was between the ninth and 



tenth [tenth and eleventh] 

 presacral vertebras rather than 

 the seventh and eighth [eighth 

 and ninth]. The most marked 

 difference between the ninth 

 and tenth [tenth and eleventh] 

 vertebras is noticeable in the 

 position of the capitular rib 

 facets. The transverse pro- 

 cess of the seventh [eighth] 

 cervical is much more slender 

 than that of the first dorsal. 

 These characters are well 

 shown in fig. 48. 



THE ANTERIOR CERVICALS.fi 



As above stated, there are 



7 [S] cervicals in the vertebral 



column of Triceratops, and it 



is probable that the number 



To give greater rigidity to the 



Fig. 49. 



-Anterior cervicals of Triceratops prorsus, No. 1S22, Yale Museum. 

 Lull. One-fourth natural size. 



Drawn by R. S. 



is constant for the different genera and species in the group. 



a In a specimen. No. 1S22, Yale Museum, the type specimen of Triceratops prorsus, a distinct suture is seen 3 to 4 mm. behind the ante- 

 rior margin of the atlas measured on its inferior face and extending upward some distance on either side, indicating that the so-called atlas 

 of Hatcher's above description is in reality the atlas and axis, while the axis of Hatcher represents the third and the third the fourth cervical. 

 The atlas is therefore reduced to a ring-like bone of somewhat greater fore and aft extent interiorly than toward its dorsal side. The axis 

 bears the neural arch and spine as described above for the atlas. On the axis of Monoclonius crassus (p. 70, fig. 78) there are distinct 

 facets, evidently lacking in Triceratops for the articulation of the first cervical rib; otherwise the anterior cervicals are quite similar in the two 

 genera.— R. S. L. 



