ZOOLOGY. 205 
3. On the Cranium of the Anomodoniia. 
The bones of the superior and palatal surfaces of the cranium 
_ of the genus Dicynodon have been described by Owen; and the 
structure of the internal walls of the palatal and nasal cavities, 
with the occipital and mandibular bones, have been described by 
Huxley, from the Ptychognathus murrayi. The relations of the 
elements of the lateral walls of the brain-case, and the attachment 
of the os quadratum, have, so far as I am aware, never been made 
out. As these points are of the first importance in determining 
the affinities of the Anomodontia, I take the favorable opportunity 
for elucidating thém, furnished by the very complete cranium of 
the Lystrosaurus frontosus, Cope, kindly placed at my disposal by 
Dr. E. R. Beadle.* 
The maxillaries articulate posteriorly and externally with the 
ectopterygoid bone. This is vertico-oblique in position, its depth 
twice as great as its length. The pterygoid, which articulates with 
it posteriorly, is seen laterally, a flat hour-glass shaped bone, the 
anterior extremity embracing the ectopterygoid by a superior and 
an inferior process, whose articular faces are at right angles with 
each other. The contracted portion presents a longitudinal exter- 
nal angle, which disappears on the posterior part of the maxillary. 
At this point the pterygoid is arched upwards and inwards: it is 
then deflected outwardly and downwards to the extremity of the 
quadratum. 
The relations of the pterygoid to the bones forming the ante- 
rior walls of the brain-case are of much interest, and throw great 
light on the vexed question of the homologies of the columella of 
the Lacertilian and Rhynchocephalian Reptiles. The adjacent 
bones may be first described. 
The presphenoid is a flat lamina with arched superior margin, 
resembling that of the Crocodilia. It extends forwards in this 
species to the line of the frontal tuberosity. The inward and up- 
ward expansion of the pterygoid behind its median contraction, 
already described, appears to be in contact with the inferior margin 
of the presphenoid. It is not likely that this expansion belongs to 
the presphenoid, though it is difficult to perceive the suture. 
The expansion is subvertical. Posteriorly it expands backwards 
and outwards, forming the fundus of a deep subvertical groove, 
and unites suturally with the antero-interior margin of a bone, 
* For description of this species, see Proceed. Am. Philos. Soc., 1870, p. 419. 
