. The Ceratopsia. Ceratopsia. 52 THE CERATOPSIA. Seen from below, as shown in fig. 53, the sacrum, presents a strong median bar formed by the united sacral centra, each of which gives rise on either side to a transverse process or sacral rib. The extremities of these transverse processes form together the periphery of an oval, so that the outline of the sacrum is an oval with the antero-posterior diameter much the longer. The inferior border of the sacrals is marked by a broad, shallow groove com- mencing with the centrum of the third sacral and extending to that of the tenth. The first sacral
. The Ceratopsia. Ceratopsia. 52 THE CERATOPSIA. Seen from below, as shown in fig. 53, the sacrum, presents a strong median bar formed by the united sacral centra, each of which gives rise on either side to a transverse process or sacral rib. The extremities of these transverse processes form together the periphery of an oval, so that the outline of the sacrum is an oval with the antero-posterior diameter much the longer. The inferior border of the sacrals is marked by a broad, shallow groove com- mencing with the centrum of the third sacral and extending to that of the tenth. The first sacral, or that vertebra which I have interpreted as a dorso-sacral, sup- ports a short, flat diapophysial process, which curves backward at its distal end and is firmly united with a similar but somewhat longer process from the second sacral. These two processes inclose be- tween them an elongated foramen. The diapophyses of the three succeeding verte- brae are likewise united at their extremities and inclose elongate foramina, as shown in fig. 55, where a superior view of the same sacrum is shown. Neither the first nor the second sacral gives off parapophysial proc- esses, and it might therefore be better to regard both these vertebrae as dorso- sacrals, as Marsh suggested. At the union of the second and third sacrals a very strong parapophysis is given off. This process arises quite as much from the sec- ond sacral as from the third, and it is from this fact that I have regarded this vertebra as a true sacral rather than a dorso-sacral. The unusually strong parapophysial proc- ess springing from the union of the second and third sacral centra is directed back- ward and outward. It is much expanded at its distal extremity, where it unites with similar processes springing from the union of the three succeeding sacral centra to form the strong acetabular bar of the sacrum constituting the superior and inner wall of the acetabulum. This acetabular bar is formed by the union of the dis
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