Prof. Owen on Dicynodon tigriceps. 237 



continued backwards almost to the squamosal. The lower boundary of the orbit, 

 so formed, increases in breadth and thickness as it advances, and assumes a 

 trihedral figure. 



The maxillary bends down from beneath the anterior half of the orbit, and 

 swells out to form the tusk-socket (21c), which is continued about an inch below 

 the trenchant alveolar border. There is no extension of that border behind the 

 tusk (c) ; that great descending tooth terminates the border of the mouth behind. 

 The diameter of the tusk where it emerges from the socket is 13 lines : it is here 

 broken off on both sides, in the specimen described ; its transverse section is cir- 

 cular, not subelliptical, as in D. Bainii. 



The nostrils, Pis. XXIX., XXX., n, are 3^ inches apart at their anterior borders ; 

 they are oval, with the long diameter parallel with that of the orbit ; the upper 

 contour is more straight through the overarching tuberosity, the lower border is 

 more curved : there is a trace of a suture descending from the middle of this 

 border which unites the maxillary and premaxillary. 



The premaxillary forms the anterior border, and where it descends, between the 

 nostrils, its middle part is slightly raised. The fractured anterior end of the pre- 

 maxillary shows the two parallel longitudinal ridges, or the fore part of the long 

 palate, PI. XXXII. 22. 



The contour of the base of the skull, PI. XXXII., forms an almost equilateral 

 triangle with the hinder angles truncate. The posterior or palatal nostril (pn) is 

 in the middle of the triangle ; it is a simple narrow elliptical aperture 3 inches 

 9 lines long, and 1 inch 9 lines broad. It is bounded behind by the protuberant 

 basisphenoid (5), which forms the narrowest part of the proper 'basis cranii.' 

 From this protuberance four bony columns diverge, like a St. Andrew's cross ; 

 two (24) are slender, subcompressed, and diverge backwards to abut against the 

 lower end of the tympanic pedicle ; two (20) are thicker, but also subcompressed 

 and rounded below ; they diverge forwards, to form the sides of the posterior 

 nostril ; these increase in thickness as they advance and unite with other bones, — 

 the palatines, — which converge to bound the posterior nostril in front ; a strong 

 buttress of the maxillary diverges from the above united bones to strengthen the 

 inner side of the tusk-socket (21). There seems to have been an oblong tuberosity 

 at the middle of each lateral border of the posterior nostril ; part at least of 

 such a projection has there been broken off". The bony palate in advance of 

 the posterior nostril is entire ; it is concave, most so from side to side, but shows 

 three thick, obtuse, longitudinal eminences ; one at its hinder half, in the middle 

 line (13) ; the other two at the fore part (22) on each side of the middle line : these 

 latter divide the fore part of the palate into three longitudinal chambers. The 

 length of the bony palate is 7 inches, its breadth 4^ inches. 



