370 



ANATOMY OF VERTEBRATES. 



apertures ; the postpalatinc foramina are in the centre of the 

 bony palate, between the palatines and maxillaries. The pala- 

 tines are large. The cribriform plate and its median ridge or 

 * crista galli' project backward into the large rhin encephalic 

 fossa. Pterygoid sinuses are formed anteriorly by the proper 

 pterygoids, and posteriorly by the ecto- and ento-pterygoid 

 plates of the sphenoid. The ectopterygoid plate is perforated by 

 an * interpterygoid ' canal, above which is a smaller ' ectocarotid ' 

 canal. The lower jaw shows a strong ridge or platform outside 

 the molar alveoli. The coronoid and condyloid processes rise 

 very little above the grinding surface of the molars. The chief 

 process of the lower jaw is the angle, a, which is broad, com- 

 pressed, and produced far backward, where it terminates obtusely. 

 The upper surface of the skull is flat, and its contour deviates 

 little from a straight line, slightly descending toward the occiput 



235 



236 



Skulls of the Chluchilla. 



and the end of the nasals. The zygomatic arch is compressed but 

 deep, especially below the fore part of the orbit. The acoustic 

 bulla? are comparatively smalL 



In Chincldlla lanigera, figs. 235, 236, the mastoid portion, h, 

 of the large tympanic bidla, «, h, m, rises to the upper surface 

 of -the cranium, as at a, but it is girt by a process of the 

 superoccipital, f, which extends outward to articulate wdth the 

 extremity of the slender process of the squamosal, e. The vacuity 

 which intervenes between the alisphenoid, parietal, and tympanic, 

 and which, in other Mammals, is closed by the more expanded 



