376 



RODENTIA. 



frontal, as far as the lachrymal. The two 

 pterygoid alas 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. 



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 intermaxillaries 

 are joined to the frontal by a suture con- 

 sisting of extremely fine and numerous 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 alae 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 the maxillary bone. The 

 points of the internal pterygoid apophyses do 

 not reach as far as the tympanum. There is be- 

 tween the pterygoid alas 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- 

 rvgoid 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 dormice 

 (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 Myoxiis mtela 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 apophysis almost covers the 

 foramen ovate. 



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 alactaga, 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 ram us 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 pacphagomys 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 

 maxillary is connected with the sphenoid. 



In the helamys the jugal is broader, and 

 extends along a little more than half of the 

 ring ; the rest is completed by the lachrymal, 

 and even by the frontal bone. The lachrymal 

 in this genus has no hook-like process : after 

 having shown itself external to the orbital 



