hatcher: diplodocus (marsh) 



33 



in the sacrals, has its origin from two instead of one vertebra as in the dorsals and 

 cervicals. The diapophysial process supported by the first and second sacrals is 

 much stronger than those of the succeeding sacrals. The pleuro-central cavities are 

 rather deep and the centra are much constricted inferiorly and medially. Between 

 the summits of the spines of the first sacral and last dorsal there is a small bone 



Fig. 10. Sacrum and ilium of Diplodocus longus Marsh ; seen from below. With anterior and pos- 

 teiior ends of sacrum reversed, pb, pubic process ; is, ischiac process ; ac, acetabulum ; b, c, d, saci'al 

 ribs ; /, /', foramina. One tenth natural size. After Marsh. 



with very rugose surface. This was present in No. 84 and in the American Mu- 

 seum skeleton. 



The Fourth Sacral. — Pleuro-central cavities not so deep and centrum less con- 

 stricted inferiorly than in the three preceding true sacrals. Rather long and strong 

 sacral ribs spring from either side of the centrum and unite by suture with the pos- 

 terior blades of the ilia. They do not coalesce with the sacral ribs of the true 

 sacrals nor do they come in contact with the neck of the ilia in such manner as to 

 take part in forming the acetabulum. The neural spine is free and there is a broad 

 diapophysial process formed as in the true sacrals by the union of branches from 

 the superior blade of the diapophysial lamina of this and the preceding vertebrse. 



