SKELETON OF RODENTIA. 369 



clevelope both external and internal plates: the outer plate is 

 mdely 2^6^'forated at its base; the inner plate terminates in a 

 liamular process. 



The common foramen opticum, the wide palatal vacuities, the 

 transversely extended glenoid cavity, and the inflected mandibular 

 angle, indicate affinity to the Marsupials. 



In a skull, seven inches long, of a Capybara, fig. 234, with the 

 entire series of permanent teeth in place, the sutures between 

 the elements of the occipital bone still remain. The compressed 

 paroccipitals, 4, are of enormous length. The basioccipital con- 

 tributes to each condyle its lower extremity. The exoccipitals 

 almost meet above the foramen magnum, the plane of which is 

 nearly vertical. The basisphenoid is perforated by a median 

 vertical canal, and is notched laterally by the entocarotids. The 

 squamosals are distinct, and essentially like those in the Hare, 

 sending backward the long compressed lamina which clamps the 



234 



Skull of the Capybara. 



tympanic and mastoid to the side of the cranium. A venous 

 sinus issues from beneath this process of the squamosal. The 

 longitudinal groove forming the articular cavity for the lower 

 jaw is angular, and completed externally by the malar bone, 26. 

 The meatus auditorius is unusually contracted, is cleft below, and 

 bounded there by two small tuberosities. The temporal and 

 orbital fossas are blended together, as in all Rodents. The lacry- 

 mal bone is of unusual size, and extends forward upon the side 

 of the face betw^een the frontal, 1 1 , and maxillary, 2 1 . The ant- 

 orbital vacuity is immense. The nasal bones, 15, are long, large, 

 and of nearly equal breadth throughout. The nasal processes 

 of the premaxillaries, 22, are coextensive with them. The sagittal 

 suture is obliterated, as well as a great part of the frontal suture. 

 There is no trace of interparietal bone. A single foramen inci- 

 sivum is situated anterior to the two large normal prepalatine 



VOL. II. B B 



