x.] RODENTIA. 181 



The zygoma is present in all, of various degrees of thick- 

 ness, but always either straight or more or less curved 

 downwards, and usually not much arched outwards. Its 

 anterior and posterior roots are formed by the maxilla and 

 squamosal respectively, the malar intervening. In many 

 cases the last-named bone extends backwards, applied to the 

 under surface of the zygomatic process of the squamosal to 

 form the outer side of the glenoid articular surface. In 

 the spotted Cavy (Caelogcnys), the zygoma has an enormous 

 vertical expansion, with a rugose or pitted outer surface, 

 and a large fossa in the inner side of the maxillary portion 

 with which the cavity of the mouth communicates in a 

 recent state. 



The lacrymal bone usually presents both orbital and 

 facial surfaces, but the orifice of the canal (lacrymal foramen) 

 is always well within the margin of the orbit. In the Beaver, 

 and many others, the facial portion is reduced to a mere 

 tubercle, and in the Hare the lacrymal is entirely within 

 the orbit. 



The j>alate of the Rodents is usually narrow. In the long 

 space intervening between the incisor and molar teeth, it 

 has no definite lateral margins, but rounds off insensibly on 

 to the sides of the face. In this region the anterior palatine 

 foramina form very conspicuous longitudinal slits, of specially 

 large size in the Hares. The portion of the palate situated 

 between the molar teeth is often very narrow anteriorly 

 and ends posteriorly in a thickened excavated border. In 

 the Hare it is reduced to a short transverse bridge, ex- 

 tending across the middle line between the premolar teeth. 

 In the Capybara and Guinea Pig the alveolar border of the 

 maxilla is very long, and presents the remarkable peculiarity 

 of extending backwards beneath the orbit to unite with the 

 squamosal at a level with the anterior border of the glenoid 



