On the Structure of the Palate in Dicynodon, and its Allies. 175 
In the Cotylosauria, as exemplified by the American genus 
Pariotichus, and by the European and South African genera of 
presumably the same order, Elginia, Pareiasaurus, and Procolophon, 
the palate is made up of a pair of large, usually tooth-bearing ptery- 
goids, a pair of small palatines and transpalatines, and a pair of 
large prevomers. The posterior nares lie by the sides of the 
prevomers, and there is no secondary palate formed. 
In the Pelycosauria, as exemplified by the genus Dimetrodon, the 
general arrangements of the palatal elements is very similar to that 
in the Cotylosauria, except that the transpalatine is either lost, or, 
as suggested by Baur and Case,* rudimentary. The posterior nares 
open by the sides of the prevomers and near the front of the palate. 
Between the Pelycosauria and the Theriodontia, of which 
Galesaurus is the type, the gap is rather a wide one, and though a 
few possibly intermediate types are known, they are known so 
imperfectly that they are of comparatively little use in the tracing 
of the evolution of the palate. Though Adlurosaurus has always 
been regarded as a Theriodont and a close ally of Galesaurus, the 
palate, so far as known, is very dissimilar, and resembles consider- 
ably that of Dimetrodon. The posterior part of the skull is quite 
unknown. It may be noted, however, that the jugal or squamosal 
does not form a descending process, as shown in the figures of 
Owen, Lydekker, and Seeley, a calcareous incrustation having 
apparently been taken for bone. In the Theriodontia, as exemplified 
by Galesaurus and Gomphognathus, the posterior nares are carried 
far back by the formation of a secondary palate. In the Anomo- 
dontia we find the secondary palate in a rudimentary condition, the 
bony plates of the maxillaries and palatines not meeting but still 
forming a firm support for the soft, fibrous palate. It seems highly 
probable that true Theriodonts will be discovered with the palate 
in the same rudimentary condition as is found in the Anomodonts. 
With the formation of a secondary palate a number of important 
changes have taken place. The element so important as a basal 
support of the skull in Labyrinthodonts and other Amphibians—the 
so-called ‘‘ parasphenoid ’’—becomes in the large majority of Reptiles 
quite rudimentary. With the formation of a secondary palate, how- 
ever, a new function is given to it, and it becomes developed as a 
median support for the palate. This median support is handed on 
through the Theriodontia to the Mammalia, and forms the mam- 
malian Vomer. The large prevomers of the Cotylosauria and the 
Pelycosauria being, with the formation of a secondary palate, no 
* G. Baur and EH. C. Case, ‘‘On the Morphology of the Skull of the Pelyco- 
sauria, &c.,”’ Anat. Anz., 1897, vol. xiii., p. 109. 
