. Bulletin - United States National Museum. Science. OSTEOLOGY OP THE ABMOEBD DINOSAURIA. 99 flesh. On the other hand, the base is extremely rugose and the only part adapted for insertion in the skin or for the attachment of other connective tissues. Further- more, specimen No. 4934 shows (pi. 2) the plates above the pelvic region retained in the rock in such an erect posture, while those more anteriorly are folded back imderneath the skeleton, a thing manifestly impossible in plates natm-aUy pro- cumbent on either side. The rugose character of the bases of the plates, as well as of the spines
. Bulletin - United States National Museum. Science. OSTEOLOGY OP THE ABMOEBD DINOSAURIA. 99 flesh. On the other hand, the base is extremely rugose and the only part adapted for insertion in the skin or for the attachment of other connective tissues. Further- more, specimen No. 4934 shows (pi. 2) the plates above the pelvic region retained in the rock in such an erect posture, while those more anteriorly are folded back imderneath the skeleton, a thing manifestly impossible in plates natm-aUy pro- cumbent on either side. The rugose character of the bases of the plates, as well as of the spines, implies an extremely tliick skin in which these were embedded. The ossicles, plates, and spines are all strictly dermal structures, for in no instance is there indication of articulation with subadjacent bones. The vasicular grooves and impressions which mark the surfaces of both plates and spines indicate that they were inclosed by a horny covering wliich in life would somewhat increase their size, as shown in figures 61, 62, 63, and 64. The primary function of this armor must have been that of defense, not, perhaps, in the sense of use as actual defensive instruments, but protective to the extent of giving the animal a most formidable appearance. It is true that the spines near the end of the tail may have been of some use as defensive weapons, but they could have been of comparatively little value for offensive purposes, although it has been contended that this was their chief function. To be effective in such a capacity, the tail should be flexible to a considerable degree, and tliis does not appear to have been the case. In the first place, the caudal vertebrae are joined by closely fitting zygapophyses, which are present nearly to the distal end of the tail; moreover, the articular ends of the centra are rather abruptly truncated, not rounded or beveled, as in those animals having a flexible tail. These structural details, combined with the series of plates along the do
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