In the marmot, the two nasal bones con stitute the middle of the upper vault of the snout. On each side of them the ascending apophysis of the intermaxillary bones, which are broader than in the hares, run up to be articulated with the frontal, the anterior border of which is transverse and only slightly festooned. The external surface of the maxillary is concave beneath a ridge, which is continuous with that of the zygomatic arch, extending as far as the intermaxillary suture. Setting off' from this point, the intermaxillary suture descends vertically to embrace the palate, of which it occupies rather less than a third. The jugal bone reaches to the anterior base of the zygomatic arch, where it articulates with the lachrymal as well as with the maxil lary bone ; it is connected with the zygomatic apophysis of the os temporis by a horizontal suture, which occupies all the second half of the arch, so that it extends as far back as the glenoid cavity, the external margin of which it fills. The lachrymal is of moderate extent in the orbit, hut is scarcely visible beyond the margin of that cavity ; besides its canal, which is altogether within the orbit, there is a small imossified space between it and the maxillary bone, situated very nee,: to the pos terior opening of the sub-orbital canal. The large space occupied by the maxillary' in the orbit keeps the lachrymal widely sepa rated from the palatine bone, with which it articulates so extensively in the Carnivora. The palatine bone occupies, posteriorly', about one-fifth of the extent of the palate. After having formed the root of the pterygoid it is prolonaed between them for about half their length6laterally ; it mounts up into the temporal region as high as just beneath the optic foramen ; it there spreads out back wards as far as the spheno-orbital foramen, and forwards, as the foramen which represents the spheno-palatine. The internal pterygoid process is not detached from the sphenoid, and terminates posteriorly in a long hook. The external pterygoid plate is very distinct ; although but little prominent, it covers the vidian foramen, and touches with its point the extremity of the maxillary.
In the squirrel, the lachrymal hook is formed by the bone of that name ; but it is also doubled by a similar unciform process, derived from the jugal. There is no membranous space between the lachrymal and the maxillary. The prolongations of the palatine bone be tween the pterygoid are shorter. In other respects the relations of the bones to each other are very similar to what exists in the marmot. _ _ In the beaver, the post-orbital apophysis of the os is very large and blunt, and all this portion of the bone very broad ; it occu Oes the greater portion of the zygomatic arch. The two nasal bones are broader in their middle, and both the intermaxillary and max illary bones reach up as far as the frontals. The lachrymals are small, especially that por tion of them which is situated without the orbit, to which the jugal bones touch. The vaulted portion of the maxillary bone is very extensive and well circumscribed in adult ani mals ; on its external margin, by the ridge, which is continuous with the inferior edge of the zygomatic arch, and internally by another ridge, which commences close to the sub orbital foramen, and mounts up on the cheek to join the ridge last mentioned. The pala
tine bone occupies in the palate a triangular space, extending as far forward as opposite the second molar tooth ; it terminates pos teriorly- between the two pterygoid alaa. The external pterygoid apophysis is of moderate length, nearly rectangular in its shape, and is pierced at its base by the vidian canal : it ar ticulates broadly with the posterior part of the maxillary in such a way as to exclude the palatine both front the orbit and from the temple. The internal pterygoid apophysis is of a hooked form, the point of the hook reaching as far as the ty mpanum.
In the orycteres, the jugal bone com mences at about the anterior fourth of the length of the zygomatic arch, and conse quently remains widely separated from the lachrymal. The ossa nasi constitute scarcely half the breadth of the snout, in which the maxillary occupies much less space, it being here the inter-maxillary which principally forms it. The last-mentioned bones mount up upon the forehead higher than the bones of the nose—a circumstance which is the reverse of what occurs in the beaver. The concavity of the maxillary beneath the base of the zygomatic arch is reduced to a slight oval depression; but its zygomatic apophysis is very long ; it is the maxillary bone and the frontal, to which it is joined by a long suture, which forms almost alone the osseous walls of the orbit. There is no lachrymal suture visible, although the lachrymal canal is distinct enough. The external pterygoid apophysis presents neither crest nor prominent angle ; the inter nal resembles that of the beaver.
In the ondatra and the water voles, the bones of the nose, which are pointed at their summits, are considerably enlarged at their inferior extremities. The intermaxillaries occupy a smaller portion of the snout than the preceding pieces, the oblique excavation at the root of the zygomatic arch exists ; but it is separated from the cheek superiorly by the vertical prolongation of the sub.orbital fora men. The malar apophysis of the maxillary extends beneath the jugal until it almost reaches that of the temporal; so that the jugal is only free at its lower margin for a very small space, and is very far removed from the lachrymal, which latter bone does not appear external to the orbit, it being concealed in the sub-orbital canal. The os palati extends into the palate as far as the first molar tooth, but is not visible either in the orbit or in the temple, in which latter region the maxillary is connected to the two sphenoids and to the frontal, as far as the lachry mal. The two pterygoid alw are well developed and of equal size ; the internal are connected with the tympanic bones, as are the external ; and by their anterior margins the latter are connected with the maxillary to a greater extent than in the beaver, so that no part of the palatine is visible externally.