OBSERVATIONS ON THE RODENTIA. 



34 



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(a) upper view of the skull of Mus giganteus. (b) side view of the anterior portion of the 



skull. (c) one of the rami of the lower jaw, inner side. 



Skull. — Zygomatic process of the maxilla broad, continued 

 obliquely upwards and outwards from the plane of the palate, 

 and divided into three parts, one of which is extended back- 

 wards to articulate with the malar bone, and complete the 

 zygoma ; the second is continued forwards in the form of a 

 compressed and almost vertical plate, which serves to defend 

 a vacuity connected with the nasal cavity. This vacuity is 

 situated anterior to the orbit, and seems to hold the place of 

 the lachrymal canal. The production forwards of the verti- 

 cal plate converts the anterior outlet of the ant-orbital fora- 

 men into a narrow slit. Connected with this narrow slit, 

 (through which the infra-orbital nerve passes), there is another 

 opening of a larger size, and the outlet of which is directed 

 upwards. Through this upper opening passes a portion of 

 the maseter muscle. The third division of the zygomatic 

 process of the maxilla is continued upwards and inwards, ar- 

 ticulates with the ant-orbital process, and completes the an- 

 terior boundary of the orbit. The superior maxillary bone 

 sends backwards a vertically compressed process almost im- 

 mediately behind the intermaxillary suture. The zygomatic 

 arch runs obliquely downwards and outwards from the ant- 

 orbital process, and is recurved at the temporal portion. The 

 glenoid cavity is of considerable extent in a longitudinal di- 

 rection, and has a moderate transverse diameter. The pala- 



