SKELETON OF PHOROEHACOS 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 (i.o.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 (lac), as just mentioned, bears a very large supraorbital plate, whicli 

 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 1 . 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 antenor 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 



1 'Ibis,' 1896, p. 6. 



