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Show 1891.] ORGAN IN THE CROCODILIA. 151 mississippiensis (figs. 1 and 2), the bullate cavity of the vomer former (vo.'") might appear to lie within the area of, and indeed to be represented by, the anterior divisions of the maxillary sinus of the latter (sn.). The distinctness in the Caiman of the two bones named shows, firstly that this cannot be the case, and secondly that the extension of the maxilla of Alligator mississipiensis into the region of the palatine lobe of the vomer of Caiman niger must have been one of the changes resulting from the loss of the latter, should that have been brought about as supposed. The premaxillo-maxillary sutures of the adult Alligator mississippiensis meet at all points, and the two pairs of bones form a conjoint and complete osseous roof to the mouth. It has, however, hitherto escaped notice that matters may be otherwise in the young of this species, for the sutures in question maybe, in them, interrupted by a couple of rounded fenestrse (fig. 6, /. pi.') having the customary relationships of the prepalatine foramina of other Amniota. On cutting away, from above, the greater portion of the olfactory organ, and then carefully dissecting off the mucous membrane and cartilaginous floor1 of the same in the largest juvenile of Alligator mississippiensis which I have examined (total length 112 centim.), I was surprised to find a couple of small sacs (jc. 1, fig. 4) lying within the embrace of the prepalatine foramina. Each is a firm and resistant structure, invested in a fibro-cartilaginous wall, and containing a soft ('? vascular) lining. I have been unable to trace any connection either between the capsules of these sacs and the cartilaginous alee of the olfactory wall, or between their central cavities and those of either the mouth or the nose. So far as I have been able to examine them, they appear to be to all intents and purposes closed vesicles, vestigial in nature. That they correspond in position with at least the anterior extremities of, and must be looked upon as directly related to, the bullate palatine lobes of the vomers of Caiman niger, I hold it to be sufficiently clear ; and it remains now to seek the clue to the remaining portions of the latter bones. On laying bare the nasal organ of any Crocodile from the side, it will generally be found, on removing the mucous membrane, that the anterior truncated extremity of the vomer is buried in a more or less powerful ligament (lg., fig. 4) which runs forwards towards the premaxillary region. Among those genera and species which I have examined, this ligament is most powerful in Osteolcemus tetraspis of W . Africa; in m y specimen of that animal it assumes the form of an upturned fold or keel, which, as viewed from the side, continues forwards as it were the body of the vomer, instead of the more general one of a cord-like structure continuous with its tapering extremity. This vomerine ligament (lg., fig. 4), as already stated, may be traced forwards into the premaxillary region ; its fibres usually there blend with those of the premaxillo-maxillary periosteum, and when (as for ex. in Crocodilus palustris, fig. 1) a " palatine process " of the premaxilla (p.p.) is present, they may be traced to an insertion into that. In the young Alligator missis- 1 A portion of this is represented in situ at ns.f. in fig. 4. |