ART. 18 



OX A NEW SKELETOISr OF DIPLODOCUS GILMORE 



11 



spines. The sixth vertebra is the first to show a decided cleft, but 

 in the present specimen it is considerably shallower than in the 

 homalogoiis vertebra of the D. carnegii skeleton. 



The relative position of the rib articulations, the size of the pleuro- 

 cels, and the shape and extent of the transverse processes are all in 

 accord with D. carnegii. The tenth dorsal is of interest in having 

 the spine intact, the first specimen found 

 showing its true relationship to the lower 

 half of the vertebra. The spine is strongly 

 inclined forward of the vertical axis of 

 the vertebra as a whole. In other words, 

 when the vertebra is placed in an articu- 

 lated position the lower half is inclined 

 backward (see fig. 2), which brings the 

 forwardly inclined spine into a nearly ver- 

 tical position. Especial mention is made 

 of this feature for the reason that in pre- 

 vious restorations the tenth vertebral spine 

 has been either restored or replaced in the 

 vertical axis, and when articulated a 

 faulty spacing of the spine top in relation 

 to others of the series has resulted. This 

 forward angulation in tlie present speci- 

 men brings about a fairly uniform spacing 

 of the spines, as would be expected. 



Mention should also be made of the 

 extreme closeness of the articulations of 

 the verte])ral centra, indicating a very thin 

 disk of cartilage between their ends. The 

 evidence afforded by this articulated series, 

 and it applies equally well to the caudal 

 vertebrae, refutes the more or less preva- 

 lent idea that in articulating dinosaur 

 skeletons the vertebrae should be percep- 

 tibly drawn apart to allow for a thick 

 disk of intercentral cartilage. 



On account of the vicissitudes of fossil- 

 ization the transverse processes of the 

 right side of the dorsal vertebrae have been crushed upward some- 

 what above their natural position, so that with the ribs articulated 

 the contour of the thorax of the two sides presents slightl}' different 

 outlines. 



The principal dimensions of the dorsal vertebrae are given in 

 Table 1. 



FiGUUE 2. — Outline of tenth 

 dorsal vertebra, U.S.N.M. 

 No. 10865, to show for- 

 ward inclination of the 

 spinous process. About 

 one-sixth natural size 



