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Show ^36 MR. J. W . H U L K E ON T H E SKELETAL [Nov. 20, transverse processes are dwarfing, and they are borne wholly on the neurapophysis distinctly above the neural suture ; no trace of sutural attachment of the transverse process is here discernible, and the process appears to be an outgrowth from the arch. Vertebrae posterior to the above are devoid of the transverse process ; their centrum retains the flattened angular form, their spinous process is more compressed, and its antero-posterior dimension is relatively greater than in the corresponding vertebras of Metriorhynchus. Sacrum.-The two sacral vertebrae differ so much from those of Metriorhynchus that they require detailed notice. 1st Sacral (fig. 6, p. 435). The centrum has a subcylindric shape. In its anterior half tbe transverse horizontal dimension is enlarged by the attachment of the transverse process. The anterior terminal surface has an obtusely elliptic outline, of which the longer diameter is horizontal. Its surface is distinctly concave in the horizontal and nearly plane in the vertical direction. The lateral lip and the adjoining part of this surface is contributed by the root of the stout transverse process, and between the upper limit of this and that part of the circumference which bounds the neural canal the lip of this surface is formed by the neurapophysis. The transverse process consists (1) of a large, stout piece of rudely trihedral, slightly fluted cross section, directed nearly horizontally outwards. This is suturally attached to the entire height of the side of the centrum in the anterior half of this latter. Upon the upper surface of this part of the process there descends from the neurapophysis a minor, thin, splint-like part which ends with a serrated margin at a little distance from the arch. The posterior surface of the centrum is nearly circular in outline and nearly plane. 2nd Sacral vertebra. Its sacrum is cylindroid. The anterior face is nearly plane, its outline circular. The posterior face is larger ; its outline is less elliptic and more nearly circular than is the anterior face of the 1st sacral vertebra. It is nearly plane in the vertical and distinctly concave in the horizontal direction. Its transverse process is suturally attached to the whole vertical extent of the lateral surface of the centrum. This attachment is separated by an interval from both ends of the latter, the terminal surfaces being formed of centrum only. The structural plane of the transverse process resembles that of the 1st sacral vertebra. Thus the sacral transverse processes rank in respect of their chief component element as ribs, so agreeing with those of Metriorhynchus ; and this remark applies also to the transverse processes of the anterior caudal vertebra. Compared with that of Metriorhynchus, the sacrum in Steneosaurus differs notably in the more nearly horizontal direction of the transverse processes, which are also stouter and relatively shorter The concavity of the anterior face of the first, and that of the posterior face of the centrum of the second, sacral vertebra is less than that of the same faces in Metriorhynchus, and the composition of these faces is also different. (No part of the pectoral girdle or fore limb has been yet procured by M r . Leeds.) |