138 ON A NEW SPECIES OF DICYNODON 
vertical vomerine septum expands inferiorly in front of the external 
nares into a mass of cancellated bone; and that mass bounds the 
nasal passages in front and above, and sends down a thin septum in 
the middle line, just as in Dzcynodon. Furthermore, the posterior 
nares are bounded externally by the palatine bones to the same 
extent in the Bird as in Décynodon; and the bone called “ inferior 
turbinal” in Birds occupies a position on the inner side of the pala- 
tine and maxillary precisely similar to that occupied by the bone 
to which I have referred above. Again, the manner in which the 
palatines and pterygoids are connected with one another and with 
the presphenoid in Décynodon is extremely bird-like. 
Many points in the structure of the mandible and premaxilla are 
very well shown by the skull of D. Murray figured in Pl. XXIII. 
[Plate 9], which displays excellent transverse sections of both the 
maxillary and the mandibular bones, not only close to the extremity 
of the snout, where, as I have already mentioned, part of the bony 
matter is altogether broken away, but at 14 inch from it, where an 
accidental fracture has taken place. The inner surface of the pre- 
maxillary bones, in front of the septum, is produced into two longi- 
tudinal ridges, which have a triangular section, their sharp edges 
being directed downwards. The upper part of the symphysial region 
of the dentary element of the mandible is developed into three very 
strong processes which fit into the interspaces left between these 
ridges—at the sides, and in the middle between each ridge and the 
downwardly inclined sides of the premawilla. 
The median ridge is $ths of an inch high and 4rd of an inch thick 
at its base. It expands superiorly and ends in a sharp edge, so that 
its section is lancet-shaped. It is separated by a deep groove from the 
lateral plates, which are slightly curved, not so long as the median 
plate, and are obliquely bevelled off internally. A section of either 
ramus shows that the upper edge of the dentary bone in this region 
is broad and produced into a thick inner and a thin outer wall, 
separated by a deep groove, which, in consequence of the convexity 
of its walls, is much narrower below than above. Inferiorly the 
dentary bone sends down a broad plate on each side. The inner of 
these remains comparatively thin and comes into contact with the 
splenial element; the outer becomes very thick where it passes the 
longitudinal ridge which marks the outer surface of the dentary bone,, 
and then, thinning, overlaps the supra-angular element. The dentary. 
element extends back for more than half the length of the ramus 
In almost all these respects the dentary bone of Decynodon is very 
