14 BULLETIN 110, UNITED STATES NATIONAL MUSEUM. 



These elements unite laterally with the alisphenoids, but in this specimen the 

 point of union is almost wholly obliterated, though it appears to pass through the 

 foramina for the exit of the third and fourth cranial nerves as shown in figure 6. 

 The openmg for the exit of the second or optic nerve is immediately below and 

 posterior to the orbitosphenoids, and is very large in this specimen as it is also in the 

 skull figiu-ed by Osborn.i 



In Tyrannosaurus the exit is divided by a filiment of bone and it appears most 

 probable that this partition is missing in the present specimens. 



Ethmoid (e.). — The ethmoid is missing in specimen, No. 4734, U.S.N.M., though 

 the sutural anterior borders of the orbitosphenoids and ahsphenoids show where it 

 joins when present. 



Parietal (jm.). — Viewed from above the parietal presents an antero-posterior 

 crest, and a transverse supraoccipital crest. The latter extends outward at right 

 angles to the central axis of the bone as two thin vertically expanded, wing-hke 

 plates much as in Tyrannosaurus and especially as in Ceratosaurus nasicornis. 

 They rise above the level of the median superior surface of the ])arietal so that when 

 seen from the rear there is a broad concave notch between them at the center 

 (fig. 4). The superior surface of the parietal in front of the transverse portion is 

 shallowly concave transversely and has a least diameter between the supratem- 

 poral fossa of 18 mm. The upper surface of the anterior end is markedly rugose 

 and transversely expanded and appears to be joined to the frontals by a nearly 

 straight transverse suture. Only the lateral sutures between the jiarietals and 

 frontals are clearly seen in this specimen, those on the superior surface being very 

 mdistinct. At the lateral sutiu-es the parietal has a transverse diameter of 37 mm. 

 The lateral borders of the superior surface are raised presenting an acute edge that 

 turns outward and upward into the more obtuse free borders of the vertical trans- 

 verse plates (fig. 5). 



The median lateral sm-faces drop abruptly downward from the superior smiace 

 and form a considerable part of the inner bomidary of the supratemporal fossae. 

 The parietals do not meet the postfrontals as in most Predentate and Sauropodous 

 dinosaurs, but are excluded from them by the lateral expansions of the frontals. 

 Ventrally, within the supratemporal fossa the parietals meet the superior borders of 

 of the alisphenoids and prootics for a short distance. Posteriorly the lower borders 

 of the transverse portion rests upon the top of the paraoccipital processes, and for a 

 short distance only an internal branch of the squamosal (fig. 4). The lower outer 

 part of the plate is produced outward and backward as a long slender tapering 

 process, that passes to the back of the inner squamosal process and to the front of 

 the paraoccipital process resting in a groove between the two, as shown in figure 4. 

 Posterior to the transverse crest the parietals are continued backward as a heavy, 

 overhanging, bluntly pointed projection, much as in Ceratosaurus. In Tyranno- 

 saurus of the Upper Cretaceous, there is no posterior projection of the parietal. 

 The upper surface of this portion is rugosely roughened. It overhangs the supra- 

 occipital with which it is firmly coalesced. The parietal, however, is excluded from 

 a lateral contact with the supraoccipital by the interposition of slender, upwardly 



1 Mem. Amer. Mus. Nat. Hist., vol. 1, pt. 1, p. 16, fig. 9. 



