3) 
234 MEMOIRS OF THE CARNEGIE MUSEUM 
is concayely bevelled below in front to receive the posterior margins of the nasals 
(Fig. 8, L. Fr. and R. F.) and grooved on its upper and outer side to receive the pre- 
frontals (Fig. 6, p. F.). The orbital margin is horizontally concave (Fig. 6) and per- 
pendicularly convex (Fig. 5). The posterior portions of the lateral margins of the 
frontals sweep downward to form the upper portion of the posterior wall of the 
orbital cavity, articulating with the alisphenoid, the postfrontals and the postorbitals. 
(See Fig. 8.) Along the posterior upper margin the frontals overlap the parietals, 
and articulate with the postorbitals on the upper margin of the process which the 
postorbitals send inwardly at the back of the orbital cavity. {See Fig. 8.) 
The Postfrontals (Figs. 5-6, 8, and 9).— The postfrontals are small bones which 
overlap the frontals and the postorbitals, forming the upper portion of the anterior 
margin or wall of the supratemporal fossa and the upper posterior margin of the 
orbital arch. They articulate with the frontals and the postorbitals and posteriorly 
with the alisphenoid on the anterior wall of the supratemporal fossa. In the speci- 
mens studied by Professor Marsh he evidently regarded the postorbital bones as form- 
ing part of the postfrontals, and united the bones under the latter name. In his 
specimen (U. 8. N. M., No. 2673) the distinctness of the postfrontals from the post- 
orbitals is shown, and is conspicuously revealed in the specimen in the Carnegie 
Museum (No. £87). 
The Postorbitals (Figs. 3-6, 8, and 9). —The postorbitals assist in forming the pos- 
terior margin and a portion of the posterior and inferior inner walls of the orbital 
cavity. One portion of the bone extends as a somewhat sharp triangular process 
inwardly, being wedged between the posterior margin of the frontal bone and the upper 
portion of the wing of the alisphenoid which clasps it and supports it underneath. 
(See Fig. 8.) Above,this process is in part covered by the postfrontal where the latter 
bone unites with the external surface of the alisphenoid to form the anterior wall of 
the supratemporal vacuity. Externally where the postorbital articulates with the 
postfrontal the postorbital sends a process backward which articulates with the 
quadrate at the outer margin of the supratemporal fossa. ‘The anterior part of the 
bone consists of a narrow process, triangular in section, running forward to a point 
where it articulates by an oblique suture with the upper posterior process of the 
jugal. The reéntering upper and lower surfaces of this process form respectively 
portions of the under surface of the posterior part of the orbital cavity and the 
upper surface of the posterior part of the infratemporal vacuity. 
The Supraorbitals (Figs. 3 and 7).— The supraorbitals are long somewhat narrow 
bones forming very largely the anterior outer margin of the orbital cavity. They 
articulate above with the prefrontals and touch the uppermost posterior prolonga- 
