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Show 266 MR. ST. GEORGE MIVART ON THE [Apr. 28, these conspicuous productions of the neural arch* ascend almost vertically, as they do in some of the posterior caudal vertebrae of Siren (fig. 8), and tend to do in those of Amphiuma. The summit of the neural arch in Urodela is never produced into a long bony Dorsal view of 23rd, 24th, 25th, and 26th vertebra? of Amphiuma. H. Hyperapophysis. c. Capitular process, t. Tubercular process. pointed process, as it is in so many higher vertebrata ; but sometimes the middle of its hinder margin projects slightly backwards, as in Menobranchus; and sometimes, as iu Menopoma, Cryptobranchus, and Menobranchus (fig. 10), the posterior part of the caudal neural arches are produced into long processes inclined obliquely backwards over the succeeding vertebrae; but they are hollow and open at the summit, and are no doubt continued in cartilage. Sometimes again the posterior part of each neural arch, whether of the trunk or of the tail, is marked by a vacuity, pit, or depression, as if for the implantation of the end of a cartilaginous rod or srmious process; this is found in Cryptobranchus and Menopoma. In Amblystoma each neural arch of the posterior trunk-vertebrae possesses two such pits placed side by side in the same transverse horizontal line as if for two cartilaginous neural spines ; and the same structure obtains throughout the caudal vertebrae. In the Axolotl the trunk neural arches Fig. 6. Dorsal view of three caudal vertebrae (sixth to eighth postsacral) of Axolotl, from specimen No. 582 c in Museum of College of Surgeons. have, from before backwards, successively longer and longer neural spines; but each one has a concave depression at its tip, as if it were continued in cartilage. The caudal vertebrae in the same form, from the fourth backwards, have each bifold neural spines, as in the trunk-and all caudal vertebrae of Amblystoma; and each is concave at its * These parts appear to correspond with those mammalian processes for which I have proposed the term hyperapophyses (P. Z. S. 1865, p. 576), and the presence of which often serves as a good osteological character for zoological groups. See Cambridge Journal of Anatomy and Physiology, vol. ii. pp. 143-154. |