x.] RODENTIA. 159 



well-marked hamular process backwards, which unites with 

 the auditory bulla in Hystrix, Lagostonms, Bathyergus, &c. 

 There are usually well-marked pterygoid fossae, and the sides 

 of the alisphenoids are often perforated by an alisphenoid 

 canal. In Hystrix the hamular process is slightly bullate. 

 The squamosal forms a considerable part of the outside 

 wall of the cranium, but in consequence of the large size of 

 the united tympano-periotic, the root of the zygomatic 

 process is thrown very forward on the side of the skull, 

 and the posterior part of the body of the squamosal which 

 unites with the occipital is reduced to a long, rather narrow 

 strip, interposed between the parietal and periotic. When 

 the mastoid bullae are greatly developed, as in Pedetes 



Per 



Fig. 55. — Side view of skull of Cape Jumping Hare {Pedetes caffer), \. Sq squamosal ; 

 Pa parietal ; AS alisphenoid ; Fr frontal ; OS orbitosphenoid ; L lachrymal ; 

 Na nasal ; PMx premaxilla ; Mx maxilla ; Ma malar ; Ty tympanic; ExO ex- 

 occipital ; Per points to the large supratympanic or mastoid bulla. 



(see Fig. 55), this does not reach as far backwards as the 

 occipital, and is a slender curved process, which clasps the 

 outside of the bulla, and appears to hold it in its place. 



The glenoid fossa is situated on the under side of the 

 posterior root of the zygoma. In its most typical form (as 



