OSTEOLOGY OF CARNIVOROUS DINOSAURS. 15 



directed processes from the exoccipitals as shown in figure 4. The greatest length 

 of the parietals is about 101 mm.; the greatest width between ends of the trans- 

 verse plates is 155 mm. 



Frontals (/.). — The frontals are relatively short, wide, and heavy, paired bones. 

 Viewed from above they are roughly triangular in outline with the anterior apices 

 truncated, as in Ceratosaurus and Tyrannosaurus, they have a great transverse 

 expansion on their posterior half, attaining a combined width of 180 mm. between 

 the fronto-postfrontal sutures. These lateral expansions unite ventrally with the 

 alisphenoids and prootics, and laterally with the postfrontals. Their superior sur- 

 faces look backward and upward and form the greater part of the anterior boundary 

 of the supratemporal fossae. 



With the exception of a small rugose area on the median superior surface of the 

 frontal near the fronto-parietal suture, the remaining surfaces are smooth and flat, 

 except the anterior ends, each of which is shallowly concave transversely and thus 

 forming a slight longitudinal ridge at their median junction. Beginning at either 

 end of the transverse fronto-parietal suture the superior surface is separated from 

 the lateral surface by sharp raised ridges that diverge as they continue forward but 

 subside before reaching the notch between the postfrontals and prefrontals. Above 

 the orbits on the ventral surface the frontals are concave antero-posteriorly. They 

 are almost entirely excluded from the upper external boundary of the orbit, by the 

 postfrontal and prefrontal bones. There is a deep, but narrow notch, between 

 those bones and their lower borders appear to have been in contact along the lower 

 part of the notch. In front of this notch the frontal bone is much thickened, with 

 a deep angular pit for the reception of a posteriorly directed projecting spur on the 

 prefrontal. Anterior to this pit the frontals send outward and forward a rounded 

 tapering process that extends free and appears to have been received between the 

 upper and lower branches of the U-shaped prefrontal. The upper process of the 

 latter bone appears to lap along the anterior side of the frontal terminating in front 

 of the fronto-nasal suture as shown in plate 4, figure 1. Anteriorly the frontals join 

 the nasals by a toothed transverse suture. An underlying projecting shelf under- 

 laps the posterior ends of the nasals as shown in figures 5 and 6. The frontals have 

 a greatest length along their midline of about 145 mm. 



Prefrontal (pf.). — A small irregular U-shaped bone found detached but in close 

 proximity to the other portions of the skull is here identified as the left prefrontal. 

 Although not exactly fitting the sutures of the frontal (due in all probability to 

 slight crushing) the presence of an angularly rounded protuberance (fig. 7), for the 

 lateral pit on the frontal and an obtusely rounded orbital border together with the 

 general agreement of the more important surfaces and articulations, renders it almost 

 impossible of mistaken identification. Viewed from the side when articulated the 

 prefrontal is U-shaped, the opening being forward. The limbs of this bone are 

 formed by two flattened, tapering processes (fig. 7), the upper being shorter and 

 less expanded latterly than the lower, which extends downward and forward, being 

 received in a groove on the internal posterior side of the lower branch of the lachry- 

 mal. The upper process continues forward, being interposed between the frontal, 

 nasal, and lachrymal, as shown in figure 1, plate 4. On the external side at the 

 junction of the two branches described above there is a concave articular surface 



