108 PROCEEDINGS OF THE NATIONAL MUSEUM. tou 55. 



in most Ceratopsian skulls. In fact, in specimen No. 5740 U.S.N.M., 

 a longitudinal ridge, that may represent a coalesced suture, runs along 

 the inside of the wall of the brain case for the olfactory lobe and if 

 correctly interpreted shows that the frontal did contribute to the 

 upper boundary of this part of the brain. By comparing speci- 

 mens Nos. 6740 and 2416 it was possil^le to determine the exact 

 extent of the articulation between the frontals and the underlying 

 sutural surfaces of the orbitosphenoids in No. 241G, as indicated in 

 figure 3, F. It will also be noted that these sutural surfaces con- 

 tinue backward over the superior surfaces of the alisphenoid and 

 supraoccipital bones, thus entirely surrounding the large median 

 opening above the cerebrum lobe of the brain. This aperture as 

 shown in figure 3 is larger than it would be normally as all of the 

 borders present broken edges. The question now arises, what bone 

 articulated with these sutural surfaces? After a study of many 

 reptilian skulls both recent and extinct it is found that the parietal 

 is the only bone that fills all requirements. As in other reptilian 

 skulls it here articulates anteriorly with the frontals ; ventrally with 

 the supraoccipital, alisphenoids, and in all probability also with the 

 prootic. Furthermore, specimen No. 5740, U.S.N.M., shows that 

 immediately behind the thickened rounded posterior end of the 

 frontal is a well-defined median foramen leading from the brain 

 case into the large air chamber above (see pin. fig. 1), and repre- 

 sents without question the interparietal or pineal foramen. The 

 position of this foramen on the median line and near the sutural 

 union of the parietal and frontal, and largely if not entirely within 

 the former bone, is in entire agreement with the location of this 

 foramen, in Dlplodocus see /. pin.^ figure 5, the living Hatteria, and in 

 the Ichthyosauria and Plesiosauria. The large air chamber or sinus 

 into which the pineal foramen opens, extends upward into the base 

 of the large horn cores with an external outlet through an opening 

 at the junction of the postfrontals with the dermosupraoccipital 

 see pt. f. f. figure 1. This opening has been designated pineal fora- 

 men by Marsh ; " the postf rontal foramen," by Hatcher ; the " post- 

 frontal fontanelle," by Lull and Lambe ; the " supratemporal fossae," 

 by Hay; and the " pseudopineal foramen," by Huene. The term 

 " postfrontal fontanelle" is perhaps the more appropriate designa- 

 tion for this opening rather than " postfrontal foramen " the use of 

 Avhich was advocated in my study of the Brachyceratops ^ skull for 

 the reason that it represents an opening not yet roofed over by bone, 

 or, in other words, the coalescence of the postfrontals with one 

 another and with the dermosupraoccipitals which had begun in the 

 earliest known Ceratopsians had not been perfected, except in old 

 individuals belonging to the last we know of the race. 



iProf. Paper 103, U. S. Geol. Survey, 1914, p. 18 



