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Show 1891.] ORGAN IN THE CROCODILIA. 149 space between the premaxillo-maxillary sutures (s.m.), to be referred to in full later on. This remarkable departure from the Crocodilian type of structure was first described by Owen *; Huxley redescribed it seven years later ~; and both writers referred it to the one isolated species named. Gray, with that mischievous originality for which he was so notorious, gave the character :i as diagnostic of the genus Jacare, and his error has been transcribed by Lydekker in the ' Palaeontologia Indica'4. It remained for Boulenger to rectify matters ; and in having done so, to show6 that the feature remains distinctive of the species (C. niger) in which it was originally described, and of none other. The leading fact that the vomers of Caiman niger are, at their point of intercalation between the premaxillo-maxillary bones, inflated and bullate (vo.'", fig. 2) was apparently known to Owen (loc. cit.) ; and a detailed account of the general relationships of these bones has been given by Huxley 6. Their remarkable characters, however, have neither received that attention which they deserve, nor have attempts been thus far made to decipher their meaning. It is precisely this gap in our knowledge which, thanks to some specimens generously placed at m y disposal by Prof. Huxley, I would now attempt to fill. The vomers of the short-snouted Crocodiliain ordinary (vo.1, fig. 1) usually commence to taper anteriorly at a point more or less vertically disposed above the maxillo-palatine suture (s.mp.). There is much variation individually and with age in respect to the exact position of the point referred to; but while it generally lies behind the suture named, it may more rarely be situated in front of it (ex. Alligator mississippiensis, fig. 4). From this point forwards, each vomer rapidly tapers and disappears on the upper surface of the palatine process of its corresponding maxilla (mx.), and with that it may become early ankylosed (ex. Crocodilus niloticus). In Caiman niger, however, the vomers (vo.1, fig. 2) pass on to the middle maxillary region (i. e. beyond that point at which these bones ordinarily cease altogether in other Crocodilia) before they commence to taper ; instead of dwindling away to a pointed extremity, they descend, becoming bullate as they do so, and, thrusting themselves between the maxillary bones, terminate as aforesaid within the palatal region. These expanded intercalary extremities of the vomers (vo."', fig. 2) may be appropriately termed their palatine lobes. The Crocodilia and Hatteria are exceptional among living Reptilia in that their " pterygoid bones send forward median processes which separate the palatines and reach the vomers " 7 ; an essentially similar condition appears to be realized in some Chelonia by the backward 1 Cat. Ost. Ser. R. Coll. of Surgeons, vol. i. p. 166 (1853). 2 Loc. cit. p. 4. 3 Brit. Mus. Cat. Shield Bept. ii. p. 25 (1872). 4 Vol. s. (iii.) p. 210 (1885). 5 Loc. cit. p. 293. fi Loc. cit. pp. 4-5. 7 Huxley, Quart. Journ. Geol. Soc. vol. xxxi. p. 426 (1875). |