Prof. Owen on the genus Dicynodon. 73 



strengthened by two short and narrow buttresses of bone on the inner side, 19', divi- 

 ding that part of the wall of the mouth into a narrow and deep median depression 

 and two wide and shallow lateral depressions, bounded posteriorly by the inward 

 prominence of the sockets of the great maxillary tusks. 



A second and more peculiar feature of the palatal region is a longitudinal ridge, 

 formed by the vomer (13), which descends from the middle line, commencing one 

 inch behind the anterior border of the intermaxillary, and after an extent of one inch 

 and a half, subsiding close to the fore-part of the posterior nasal aperture. The 

 vomerine ridge, at its middle part between the sockets of the tusks, is about half an 

 inch in depth : it must strengthen the palatine vault or arch of bone, just as similar 

 appendages of a Gothic roof are introduced to give additional strength as well as or- 

 nament. We may therefore regard this structure, which I have not observed in any 

 recent Saurian, as physiologically related to the uses of the tusks of the Dicynodon. 



There are no clear or well-defined traces of anterior palatine apertures in the pre- 

 sent fossil ; an unbroken vault of bone seems to extend from the edentulous border of 

 the intermaxillary and the great maxillary alveoli to the single median vacuity {p'), 

 which I take to be the posterior outlet of the nasal cavity. This is of an oval form, 

 one inch two-thirds long, one inch broad, with the great end behind : there is a 

 shallow longitudinal depression on each side of the fore-part of the aperture ; the 

 inner border of the depression, formed by the palatine (21) and ento-pterygoid 

 is produced into a ridge, but supports no teeth ; the outer boundary of the 

 depression is formed by apparently the os transversum or exo-pterygoid (23), 

 which thence extends outwards and forwards to abut against the back part of the 

 alveolar border of the maxillary. In the place of the depressions, we find in some 

 Lacertians, as Varanus niloticus, perforations, corresponding with the larger vacui- 

 ties in the same part of the palate in the Crocodilians. If, as appears from the 

 carefully exposed palatine surface of the fossil under description, that surface is 

 imperforate anterior to the large median aperture {p'), the condition of the bony 

 palate is essentially the same as in the genera Testudo and Chelone ; but the ante- 

 rior, imperforate tract of bone is much more extensive in Dicynodon. In some 

 Emydes, and in Trionyx, where the palatal bony roof is of greater extent, it is per- 

 forated by an anterior median aperture just behind the intermaxillary border. An 

 analogous aperture is present in the Crocodilians, which is indubitably not the 

 case with the Dicynodon. 



The palate of all the existing Lizards that I have examined or found figured in 

 books, presents two anterior palatal apertures besides the single large median 

 posterior vacuity ; and most of them have likewise two lateral vacancies, bounded 

 internally by the vomerine and palatine bones, externally by the maxillary bones : 

 the Varani have, besides, the pterygoid lateral perforations. Of none of these cha- 



