OF TRITYLODON LONGAVUS. LAT. 
on its orbital surface by a lacrymal foramen, and articulating below 
with the anterior end of the malar bone, 26. ‘This defines the lower, 
and almost the anterior half of the border or boundary of the orbit, 
which was not completed behind ty bone. The frontals contract as 
they extend forward, articulating with the nasal, 15, and maxillary _ 
a, bones, between which are their pointed terminations. 
The nasal bones, 15, at first narrow and convex, gradually expand 
and contribute the upper half of the border of the external nostril. 
This is terminal (fig. 4), opening directly forward with a slight 
inclination to the lower border, which is contributed by the pre- 
maxillaries, 22. In their forward course the nasals articulate 
laterally with the maxillary bones. The anterior termination of 
the nasals, which slightly overhang the aperture, has suffered 
abrasion. 
The facial part of the maxillary extends from the lacrymal, 
expanding as it advances to unite above with the frontal and nasal 
bones, and swells outwardly where it joins the premaxillary: it is 
separated from the nostril by the union of that bone, 22, with the 
nasal. The alveolar part of the maxillary (fig. 2, 21) extends from 
the maxillo-malar suture backward, supplying a partial floor to the 
orbit and a sufficient case for the series of large and complex 
grinders (fig. 2, 1-6). 
The premaxillary (fig. 3, 22) curves upward and backward, ending 
on the upper surface of the skull in a point, where it is interposed 
between the nasal and maxillary (fig. 1); it expands as it descends, 
advancing, to form the thick smooth convex side wall of the nostril, 
bulging outward to complete the socket of the large anterior incisor ; 
mesiad it contracts to join its fellow, the pair forming at their 
junction beneath the nostril a short pointed process (fig. 4). 
The premaxillary part of the bony palate (fig. 2) is short, convex 
lengthwise, concave across. The terminal expansion of each pre- 
maxillary is occasioned by the formation of the socket of the 
large incisor,21. Behind each socket is a much smaller one, 2 2. 
Behind these sockets may be discerned a trace of the transverse 
suture between the palatal portions of the premaxillary and 
maxillary bones. The mid-palatal suture of the maxillaries is 
slightly produced for a short extent, and this region of the bony 
palate is bounded laterally by ridges dividing the palatal from the 
facial parts of the maxillary. These lateral ridges slightly converge 
as they pass backward to terminate each at the fore wall of the 
socket of the anterior molar tooth. The extent of this ‘ diastema,’ 
or toothless interval between incisors and molars, is shown in fig. 2. 
The intermolar part of the bony palate is moderately concave length- 
wise, rather more deeply across: it terminates between the fiith 
and sixth molars: at least careful removal of matrix failed to 
expose further osseous extension : and the cavity so exposed (Pl. VI. 
fig. 2) I take to indicate the hinder or palatal nostril, n’, which 
opens obliquely backward. 
The tracts of bone continued backward from the orbits (fig. 3) ex- 
pand vertically, and converge, leaving a contracted cranial or cerebral 
Le 
