12 



PROCEEDINGS OF THE NATIONAL. MUSEUM 



VOL, 8t 



Table 1. — Comparative measurements of dorsal verteirae of Diplodocus 



Sacral vertebrae. — The complete sacrum is present with both ilia 

 in position. It consists of five ankylosed vertebrae, all of which are 

 coossified with and give support to the ilia. The conditions found 

 to obtain in the sacral region are very similar to those described by 

 Hatcher ^^ in Diplodocus carnegii, differini]^ only in minor details. 

 The neural spines of the three middle sacrals have coalesced into a 

 single spine, which in this individual is especially massive, being 

 subequally expanded transversely and anteroposteriorly. The pres- 

 ence of three separate bony ossicles interposed between the tops of 

 the spines is unique, as but a single one has previously been found. 

 The most anterior of these ossicles lies between dorsal 10 and sacral 

 1 ; the second between sacrals 1 and 2, and the third between sacrals 

 4 and 5. 



These ossicles are massive, subtriangular in shape, and conform 

 nicely to the interspace between the spines. Their rugose surfaces 

 indicate their inclusion in cartilage, as there is no indication of 

 actual contact of the bone surfaces. It seems quite probable that 

 similar ossicles were present between the spines of the three now 

 coossified, but all trace of their union is obliterated, so that one can 

 not be sure of the condition suggested. 



Caudal vertehyme. — The caudal region has been fully described by 

 previous authors, and at this time it appears only necessary to call 

 attention to certain details displayed for the first time in Diplodocus 

 by this particular individual. 



In their general proportions, development of laminae, and pro- 

 gressive structural changes, the caudal vertebrae of this specimen 

 agree very closely with the American Museum specimen of Diplo- 



" Mem. Carnegie Mus., vol. 1, p. 30, 1901. 



