In the rats, properly so called, the bones of the nose likewise increase in breadth, towards their extremity, to an extent which varies in different species. The in terin axillaries are joined to the frontal by a suture con sisting of extremely fine and munerous in dentations : they form scarcely, the half of the snout, comprehending the vault and the roof of the zygomatic arch, which is here directed much further outwards, and is separated from the rest of the cheek by a deep groove ; in front of this groove the maxillary is ex cavated into a sort of pouch, its zygomatic process is very long, the jugal bone short and slender. The lachrymal is entirely contained within the orbit, no part of it being visible at the point of union between the frontal and maxillary upon the margin of the orbit, but a prominent hook-process, situated within the edge of the orbital cavity. The palatine fills up half the space situated between the fora mina incisiva and the hinder margin of the palate ; its pterygoid wings,moreover, are con siderably prolonged between those of the sphe noid, but the external pterygoid aim of the latter bone entirely cover it externally by passing to join the maxillary, as in the ondatra, never theless it shows itself in the floor of the orbit embraced in a fissure of themaxillary bone. The points of the internal pterygoid apophyses do not reach as far as the tympanum. There is be tween the pterygoid alx a membranous space.
In the gerbilles, the bones of the nose and the intermaxillaries are prolonged in front, a little beyond the incisor teeth ; the suture be tween the intermaxillary is composed of radi ated indentations; the maxillary bone expands into a very thin lamina at the anterior margin of the orbit ; and this lamina is continuous with another given off at this point by the lachrymal ; the jugal bone is very slender ; the palatine runs forward in the palate as far as the middle of the first molar tooth ; posteriorly it is not visible in the orbit, the articulation of the external wing of the sphenoid with the maxillary concealing it on the outer side, as in the preceding genera. The internal pte rygoid apophysis reaches as far as the tym panum.
In the hamsters, the bones of the face closely resemble in their disposition those of the rats properly so called. In the dornziee (Myoxus), as in the gerbilles, the end of the snout projects beyond the incisor teeth ; and the intermaxillary bone occupies a large portion of the snout ; whence it results that it is pro longed upwards by- a short ascending branch. In Myoxus nitela the maxillary presents be neath the sub-orbital hole a prominent tubercle, which does not exist in the dormouse (Myoxus Glis). Both of them have a mem branous space in each of their palatine bones ; and, moreover, this bone retakes its usual position between the maxillary and the sphe noid upon the outer side of the pterygoid ala, so that the latter is only in contact with the maxillary by its apex, nearly in the same manner as in orycterus.
In spalax (the rat mole), the bones of the nose become at an early period consolidated together for a portion of their length, they expand inferiorly, and are proportionally of larger size, than in orycteres. The process of the maxillary which surrounds the infra-or bital hole is broad and thin ; the jugal is very slender, and does not at all contribute to form the inferior rim of the orbit ; the ex ternal pterygoid apophy sis almost covers the foramen ovale.
In the rhizomys of Sumatra, the fronto maxillary suture continues the line of union between the frontal bone and the other bones of the face. The bones of the nose are sepa rate, and the frontals consolidated together : the bones of the nose are here of a triangular form. The lachrymal is entirely contained in the orbit ; the jugal, which is broad, occupies the centre of the zygomatic arch ; the palatine is small, and of a triangular shape in the re gion of the palate; it is not visible in the orbit, on account of the union between the ala of' the sphenoid and the maxillary bone, which is as extensive as in the ondatra. The in ternal pterygoid apophysis is prolonged into a long hook.
In the jerboa, properly so called, and in the alaetaga, the jugal ascends at a right angle along the posterior edge of the great pre-orbital ring as far as the lachrymal, with which it is connected. In the jerboa this part is enlarged into a broad lamina ; in the alactaga it is a simple, stem-like process. The maxillary takes beneath the sub-orbital hole the form of a large ring, which might almost be mistaken for an orbit. The lachrymal forms towards the upper part of this ring a broad hood-like process. The bones of the nose cover the whole upper part of the snout, and are even bent a little into a tubular form at their extremity. The ascending ramus of the intermaxillary is very narrow at its origin, between the nasal and the maxillary ; it after wards spreads out as it approaches the frontal, with which it is connected on a level with the bones of the nose by a finely serrated suture.
In the p.xphagonzys the jugal is broad, it gives off a post-orbital apophysis, and does not mount along the pre-orbital ring. The face of this animal offers a very remarkable peculiarity. A cylindrical tube, bent into an arched shape, traverses the great ring, and is applied beneath the orbit against the alveolar arch. In this genus, as in the preceding, the rnaxillary is connected with the sphenoid.