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Show 358 PROF. G. B. HOWES ON HATTERIA. [May 6, original specimen (Bullet. Mus. Belg. t. ii. p. 185), and as doubts had recently been thrown upon its existence by Cornet and Smets (cf. Dollo, Zoolog. Jahrb. Jena, t. iii. Anat. p. 433), he deemed it advisable to examine the material at his disposal. Six spirit-specimens were accordingly examined ; five of them showed that, as with the examples of Baur (Zoolog. Anz. 1886, p. 1) and Dollo, the "pro-atlas" was present and bilaterally symmetrical, while in the sixth (viii.) it was present on the right side only, having been apparently removed on the left. He fully acquiesced in Dollo's criticisms of the statements made by Cornet and Smets and of the views of these and other observers, and agreed with them in regarding the " pro-atlas" as (I.e. p. 437) "without doubt constant in Hatteria"; he, moreover, believed that it was invariably present on both sides, and that in those examples in which it had been detected on one side only, it had been either lost (as suggested by Albrecht, /. c. p. 192) in maceration, or incautiously removed. Referring to the general relationships and morphology of the "pro-atlas," he pointed out that the former are most nearly in harmony with the supposition that it represents the arches of a vestigial vertebra. It articulates upon the skull ; and in its relations to the episkeletal muscles it repeats the conditions of the atlas ; its arches are preformed in cartilage (cf. Baur, Amer. Nat. 1886, p. 288); they lie, like those of a normal vertebra, buried in the dorso-lateral (occipito-atlantal) ligaments (fig. 3) of the vertebral column, and their separation in the dorsal middle line is but an exaggeration of that so characteristic of the atlas in Hatteria, Crocodilia, and many other Sauropsida. He stated that he was inclined to accept Dollo's declaration of homology between those various structures, which have been described in leading classes of Vertebrata, to which he collectively applies the term " pro-atlas" (for genera and species see Dollo, Bull. Mus. Belg. t. iii. p. 127, and Zoolog. Jahrb. /. c.) ; and that the views of that author appeared to him to be in complete harmony with Froriep's important discovery (Archiv f. Anat. u. Phys., Anat. Abth. 1882, p. 279) of the vertebral nature of the occipital segment of the skull, and with those of Sagemahl (Morpbolg. Jahrb. Bd. ix. p. 177), Jungersen, and others which bear upon it. Vomerine Teeth.-These were originally described by Baur (Zool. Anz. 1888, p. 85) iu a young individual of 210 millim. total length, the skeleton of which was still largely cartilaginous. Prof. Howes's interest in the question had been heightened by a statement of Mr. Boulenger's to the effect that he had not been able to find vomerine teeth in any of the skulls of Hatteria in the Natural History Museum. He had examined the palates, in all, of nine specimens, details of which were given as follows :- Specimens examined. Prepared skeletons. Vomerine teeth i. 200 mm. ii. 220 mm. "Pro-atlas" absent. present, the right the larger. |