SKELETON OF PHORORHACOS INFLATUS. 59 
outward, terminating above in a prominent cristiform ridge on the ventral surface of 
the postorbital process. 
The orbits are very large; they appear to be divided one from another by a complete 
bony septum (7.0.s.), or there was at most a small vacuity in front of the optic foramen. 
These latter appear to be confluent, and lie on exactly the same level as the trigeminal 
foramina. 
In the upper posterior region of the orbit there is a deep depression, which no 
doubt lodged a gland; from this a shallow groove runs forward along the upper edge 
of the interorbital region. This groove marks the course of the olfactory nerve, and 
immediately above it the great penthouse-like roof of the orbit arises. The whole of 
the inner and posterior part of this is formed by the orbital plates of the frontals, 
while externally it is completed by the enormous supraorbital plate of the lachrymal, 
which in this specimen has been somewhat displaced downward on both sides, so that 
the skull, seen from above, appears as if it possessed large supraorbital depressions, 
such as occur in the Petrels, &c.; though, as a matter of fact, no such depressions 
existed (see Plate XIV. and Plate XV. fig. 2). 
The lachrymal (ac.), as just mentioned, bears a very large supraorbital plate, which 
extends nearly to the postorbital process, terminating posteriorly in a blunt rounded 
angle. Its inner border was closely applied to, if not united with, the outer border of 
the frontal, and its outer border forms the upper margin of the orbit. Anteriorly its 
ventral surface is deflected, and the body of the bone turns inward and downward, and 
is produced ventrally into a nearly vertical bar of bone, which in its ventral portion is 
flattened laterally to a thin plate, and at its lower extremity articulates with the upper 
border of the jugal. A little above its middle point this bar has a small backwardly 
projecting process, but there does not seem to be any trace of a separation into two 
elements at this point, such as was formerly suggested!. The form and relations 
of this structure are almost precisely the same as in Serpentarius, or even more 
Accipitrine, as in the Eagles, e.g. the Harpy Eagle; and I can see no justification for 
Ameghino’s description of the orbit as open anteriorly in Phororhacos any more than 
it is in the birds just mentioned, in which also this process reaches the jugal. 
In front of the preorbital process of the lachrymal is the antorbital fossa, which 
is triangular in outline, its anterior and upper angles being rounded off. Its anterior 
border seems to be formed by a downgrowth of the nasal meeting an upward process 
from the maxilla; there are, however, a number of cracks in this region, which render 
its interpretation difficult, but by comparison of the two sides some degree of certainty 
can be attained. 
‘The nasals consist of a posterior body, which unites behind with the frontals and 
supraorbitals ; but it cannot be determined whether the two meet in the median 
| «Ibis, 1896, p. 6. 
