240 



PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxvi. 



upper median face. The lateral surfaces of the centrum are evenly 

 concave antero-posteriorlj'. The small, circular neural canal extends 

 down somewhat obliquely from front to back, a peculiarity present 



in a few of the succeeding 



=^-a^.zyff- vertebra?, and appears to indi- 



cate a rapid dropping of the 

 tail as it leaves the sacrum. 

 The neural arch is low and 

 firmly attached to the cen- 

 trum by broadly expanded 

 pedicles. The transver.se 

 processes spring from the 

 sides of the neural arch just 

 above the neuro-central su- 

 ture (see 6-', fig. 18), extend- 

 ing out at right angles to 

 the centrum on a level with 

 the neural canal, not so high 

 above it as shown in Marsh's 

 restoration of C (lis par (see 

 Plate 18). 



It has also been determined 

 from these specimens that 

 Marsh's rei:)resentation of 

 this region on Plate 50, 

 ^ Dinosaurs of Xorth Amer- 

 ica," is in error in the fol- 

 lowing respects: The neural 

 arches are too high; the 

 .spinous processes are too 

 straight and do not decrease 

 in height rapidly enough 

 after leaving the sacrum ; 

 their bases should show the 

 antero-expansion of the base 

 of the spine, and their tops 

 should be directed at more 

 of an angle posteriorly. The 

 spinous process of the .second 

 caudal rises as a high, thin, 

 backwardly directed blade 

 of bone (see .s, fig. 18), ter- 

 minated by a slightly thickened end, which is gently rounded antero- 

 posteriorly. There is a prominent widening of the base of the spine 

 by the development on the anterior margin of a thin septum of bone 

 which subsides rapidly above. This anterior development of the 



a^yg 



p^yQ 



Fig. 17. — Saceuji of CAMPTOSAunr.s muiwNi. 

 HOLOTi'PE. Cat. No. 4282, U.S.N.M. ; \ nat. 



SIZE ; SEEN from ABOVE. fl. Zyg, PREZTGAPO- 

 PHYSES ; (I, DIAPOPHYSIS OF 16tH OK SACRO- 

 DORSAL ; (1', DIAPOPHYSIS OF SACRAL ONE ; f, f'-, 

 FOKAMIXA BETWEEN THE SACRAL RIBS ; p. Zyg. 

 PO.STZYGAPOPHYSES ; S-y, 8n, Ss, *S't, ^5, SACRAL 

 VERTEBIi-T': ONE TO FIVE. RESPEl'TI VELY ; 8c, 

 .SACRO-CAUDAL ; 8(1, SACRO-DORSAL ; <SY. SACRAL 

 RIBS ; tr, TRANVERSE PROCESS OF SACEO- 

 CAITDAL. 



