326 THE AMERICAN NATURALIST. [VoL. XXXII. 
as seems to be very probable if not absolutely demonstrated, 
it is certainly the most highly specialized, in the possession of 
strongly developed intermediate tubercles on the upper molars, 
which are only feebly developed in Diademodon. 
The skull is partly known in the genera Gomphognathus, 
Microgomphodon, and Trirachodon. As in the Cynodontia, the 
temporal fossze are separated by a more or less distinct sagittal 
crest, less prominent than in the Cynodontia because of the 
reduction of the temporal muscles. As in the Cynodontia, the 
zygomatic arch is formed by the malar and squamosal bones, 
and the orbit is separated from the temporal fossa by the post- 
orbital (postfrontal, Seeley) bone. There are two well-defined 
occipital condyles at the back of the base of the skull, united 
to each other inferiorly in a way that is closely paralleled in 
some mammals. The occiput is triangular and more or less 
concave. It lacks the large lateral foramen which distinguishes 
the occiput in the carnivorous Cynodontia. Externally at the 
sides of the occiput there is a deep notch where the squamosal 
bone is given off to the zygoma. The malar bone extends 
behind the orbit as in the mammals, and unites with the 
squamosal to form the larger part of the zygoma, developing a 
small descending process. The hard palate formed of the 
maxillary and palatine bones terminates in the middie of the 
molar region. Behind this, sharply distinguishing the palatal 
region from that of the mammals, there is a transverse descend- 
ing arch apparently composed of the transverse bones, extending 
downwards so that it abuts against the rami of the mandibles, 
as in the Crocodilia, Rhyncocephalia, and Lacertilia. The most 
important resemblance to the Cynodontia is the degenerate 
condition of the quadrate bone, which, in the words of Seeley, 
“appears to be reduced to a small ossicle imbedded in the 
squamosal bone, but exposed in its posterior aspect behind the 
articular condyle of the lower jaw, into which it appears to 
enter.” 
The dentition is highly specialized. The incisor teeth are 
small and pointed. The canines are reduced in Microgompho- 
don, practically resembling the incisors. In other forms they 
are large, compressed, with serrated margins, as in the cyno- 
