On the Structure of the Palate in Dicynodon, and its Allies. 171 
The examination of a beautifully weathered palate in the Port 
Elizabeth Museum, which I have elsewhere described as the type of 
Oudenodon truncatus,* shows that almost the whole of the palatal 
surface of the hard palate is formed by the premaxillary, and a 
transverse fracture through the median ridge reveals that the ridge is, 
if not morphologically a part of the premaxillary, at least an element 
completely anchylosed to the premaxillary. Figure 3, Pl. XXV., repre- 
sents semi-diagrammatically a transverse section through the median 
ridge of Oudenodon. It is here seen that though the maxillary has 
large palatal plates they are to a great extent overlapped by the pre- 
maxillary plates. Above the palate is seen the median internasal 
plate of the premaxillary. This median plate extends from the 
anterior part of premaxillary backwards as far as the palatal por- 
tion, and is closely articulated posteriorly with the large median 
plate of the true vomer. In Dicynodon the structure of the pre- 
maxillary, so far as I have been able to observe, is quite similar. 
In Ptychosiagum | the general arrangement of parts is similar to 
that in the more normal genera, though the proportions differ some- 
what. Figure 1 represents the palate of Ptychosiagum. Here as in 
Dicynodon and Oudenodon the palatal plates of the premaxillary 
overlap the plates of the maxillary and form the larger portion of 
the bony palate. The median ridge is much more conspicuous than 
in the less specialised genera, projecting very considerably from the 
rest of the palate. It passes backwards a short distance beyond the 
limit of the lateral palatal plates and articulates with the anterior end 
of the vomer by an interdigitating suture. Only a small portion of 
the maxillary shows on the palate between the premaxillary and the 
anterior part of the palatine. It forms a distinct though imperfect 
secondary palate, its inner edge not quite meeting the median ridge. 
Immediately behind the median ridge is seen the well-developed 
vomer. 
Figure 2, Pl. XXV., represents a median section of the snout of 
Ptychosiagum, and shows very clearly the structure of the internasal 
septum. The internasal ridge of the premaxillary is very greatly 
developed, its depth being about equal to the antero - posterior 
measurement of the premaxillary. Immediately behind the large 
* R. Broom, ‘‘On Two New Species of Dicynodonts,” Ann. South African 
Museum, vol. i., pt. 3, p. 455. 
+ As Owen’s name Ptychognathus is preoccupied by Stimpson, 1858, for a 
Crustacean genus, I have adopted provisionally Lydekker’s name Ptychosiagwm, 
1889. Cope had, however, described a species of this same genus in 1870 under 
the name of Lystrosaurus frontosus, and if Cope’s name is not preoccupied it will 
take the place of Owen’s name. When writing in the bush away from libraries it 
is impossible to decide on questions of nomenclature. 
