SKELETON OF RODENTIA. 371 



squamosal, is here, tlirougli the retention by that bone of its pri- 

 mitive form as a diverging slender ray, left uncovered. The 

 meatus is long, wide, infundibuliform, Avith the outlet obliquely 

 truncate and directed upward and a little backward : the petrosal 

 bulla, m, continued from its lower extremity, seems to describe 

 a semicircular curve downward and backward, circumscribing 

 the large foramen, which directly pierces the bulla beneath the 

 meatus. The paroccipital is slender ; its point does not extend 

 below the level of the tympanic bulla. The articular groove for 

 the lower jaw is deep, and is completed externally by the malar, 

 k. An almost circular piece seems to be cut out of the zygoma, 

 above the junction of the malar with the squamosal. The facial 

 part of the lacrymal extends half-way across the antorbital root of 

 the zygoma, where the zygomatic part of the maxillary articulates 

 by suture with the nasal process of the same bone, circumscribing a 

 large antorbital vacuity. The nasal processes of the premaxillaries 

 slightly expand at their extremities, which extend beyond the 

 corresponding ends of the nasals, /. A strong and long oblique 

 ridge traverses the inner side of the ramus of the lower jaw. The 

 outer side is irregularly swollen by the bases of the sockets of the 

 curved molars, but has not the distinct ridge which characterises 

 that part in the C a vies. 



In the skull of an adult 237 



Paca ( Coelogenys, fig. 237), 

 with the mature dentition, 

 the sutures between the 

 elements of the occipital, as 

 likewise the sagittal suture, 

 are obliterated. There is no 

 trace of interparietal bone. 

 The basioccipital, basisphe- 

 noid, and presphenoid have sk^ii ,f ^i.^ coeiogenys. 



coalesced to form a continu- 

 ous bony floor for the cranial cavity. The third division of the 

 fifth notches the alisphenoid posteriorly, the foramen ovale being an 

 irregular fissure between the ali- and basi-sphenoids and the petro- 

 sal. The petrotympanic is free from tlie squamosal, and rather 

 loosely suspended beneath the overarching posterior lamella of the 

 squamosal, which bends down external to the mastoid and paroc- 

 cipital, 4. The malar, 26, is a slightly curved plate, twice as deep 

 as it is long, and forms the posterior third part of the zygomatic 

 expansion, the rest being formed by the maxillary, 21, which is 

 unusually and enormously developed. The squamosal forms only 



B B 2 



