NO. lOOG. OSTEOLOGY OF CAAII'TOSAURUS—CilLMORE. 237 



the sacral centra, although they have been described as being with- 

 out it."* 



The five sacrals give support to five sacral ribs on each side. These 

 ribs, excepting the fifth, are supported intorvertebrally by rough 

 sutiiral areas on their superior junctions, the main support being 

 given by the posterior vertebra of each pair. 



The neural processes are either missing or only represented by 

 detached fragments in C. hroumi, but in order to make the descrip- 

 tion complete, these will be described froui the holotype of C. nanus, 

 Cat. No. 2210, U.S.N.M., which has the anterior three unusually 

 well preserved (see fig. 39). Xs in C. dispar, there are only four 

 true sacrals in C. nanns. 



The neural arch in sacral one is somewhat higher than the last 

 dorsal, with a much enlarged neural canal. In sacrals one, two, and 

 three, the arches are contracted antero-posteriorly and expand out- 

 Avardly into strong buttresses which, with the sutural surface on the 

 centra, give support to the sacral ribs. This antero-posterior con- 

 traction of the pedicles leaves vertical, elongate cavities opening into 

 the enlarged intervertebral chamber of the neural cavity for 

 the exit of sacral nerves. The arches are united by heavy and closely 

 fitting zygapophyses. The postzygapophyses are shifted well forward 

 over the center of the centrum. 



The neural spines are flattened plates which, as they rise above 

 the arch, gradually expand antero-posteriorly, terminating in an end 

 slightly thickened transversely. The spines remain about the same 

 height throughout, all being inclined somewhat backward. In this 

 specimen the sj^ines are distinct and show no indication of fusion, 

 as is indicated by Marsh's first restoration of this region in C. clispar. 



The diapophyses of sacral one, in specimen No. 2210, are consid- 

 erably modified from the thoracic type. They join with an outward 

 development of the pedicle, forming a continuous vertical articular 

 face or buttress, with which the upper portion of the sacral rib ar- 

 ticulates. The first is the heaviest of the series, and this sacral rib 

 was undoubtedly the chief support for the ilium. The diapophyses 

 of sacrals two and three are developed in the same manner, although 

 lighter in construction. 



In the sacrum of Cat. No. 4282, U.S.N.M., sacral ribs one and two 

 were still in position and completely ankylosed with the vertebra? 

 (see S7\ fig. 17). These ribs are short, compressed plates with ex- 

 panded articular ends. Inferiorly the first rib articulates with the 

 centra of the last dorsal and first sacral, more especially the latter. 

 Above, the rib has become coossified with the buttress and diapoph- 

 ysis of sacral one. This broad, vertical plate is directed outward 

 and somewhat backward. Its outer end is expanded antero-posteri- 



"Amer. Journ. Sci., XLVIII, 1894, pp. 88, 89. 



