16 



BULLETIN 110, UNITED STATES NATIONAL MUSEUM. 



wliich meets the posterior border of the laclirymal. The rounded spur-like projec- 

 tion of the frontal was received between the branches on the internal side of the bone. 

 Its heavy vertically rounded posterior border forms the anterior boundary of the 

 narrow but deep notch above the orbit. 



So far as I am aware the prefrontal bone has not before been recognized in the 

 Theropodous dinosaur skull except in Tyrannosaurus, where it is much more reduced 

 and occupies a more central position, barely reaching tiie nasals. 



Postfrordal + postorUtal {po.f.). — The right postfrontal remained firmly attached 

 to the posterior portion of the skull, the left was found detached, so that the two 

 bones give a very accurate conception of its form ami" relationships. It is a triradi- 

 ate bone, with one short heavy process that extends inward and articulates with the 

 frontal by a deep interlocking suture; a second slender, tapering, posteriorly directed 

 process that is received in a deep lateral groove, on the anterior extension of the squa- 

 mosal, these forming the upper temporal bar; the third, the longer one of the three, 

 also a tapering process, extends downward and joins by a lapping suture the 

 superior process of the jugal, thus forming the postorbital bar which separates 

 the orbit from the infratemporal opening. This process, as in many of the Preden- 



FiG. 7.— Left prefrontal of antrodemus valens Leidy. No. 4734, U.S.N.M. J NAT. size. (.\) External view. (B) 

 Internal view. /, protuberance on posterior end which enters a pit on side of frontal; s. p, superior process; 

 V. p, ventral process. 



tate dinosauria, is trihedral in cross section. From the superior border to the end 

 of the inferior branch it measures 190 mm. in length. The greatest antero-posterior 

 diameter is 160 mm. Its principal features are well shown in plate 4, figures 1 and 2. 



The bone here identified as the postfrontal is called by some authorities the 

 postorbital and by others the postfrontal. It undoubted^ represents a complex 

 of the two bones as recognized hj Osborn, for on the median internal side posterior 

 to and below the sutural surface that meets the frontal is an elongated, cupped 

 articular depression that receives the outer end of the alisphenoid as in all known 

 dinosaurian crania. In those skulls in which the postfrontal and postorbital bones 

 are found as distinct elements, this cupped depression for the reception of the outer 

 end of the alisphenoid is always in the postorbital bone. It would appear therefore 

 that the suture separating these bones, here coalesced, must be above this cup-like 

 depression. 



Prootic {pro.). — The prootic is wedged in between the parietal and occipital 

 segments, and widely exposed externally. It bounds the auditory fenestra sujieri- 

 orly and also the foramen ovale. Osborn hfes shown that it also contributes to the 

 boundary of the foramen for the exit of the seventh or facial nerve, but usually in 

 dinosaurian crania this foramen passes directly through the prootic bone. On the 



