692 Bulletin American Museum of Natural History. [Vol. XIX, 



the median chamber by vertical pillar-Hke bones, one on either 

 side, which serve also to support the antero-intemal portions of 

 the horn cores. The floor of the second or largest chamber is 

 deeply excavated, and it is this chamber which communicates 

 with the horn-core sinuses by openings in the lateral walls. 

 The posterior chamber, lying just beneath the fontanelle, is 

 small and round, and in the specimen in question has a small 

 pencil-like bone running obliquely from the left lateral wall to 

 the floor, after the manner of a flying buttress. There is no 

 indication of a pineal foramen opening into the brain case 

 which lies directly beneath the above sinus; hence the Cera- 

 topsia agree with other Dinosauria in this respect. The post- 

 frontal fontanelle closes in old animals, as in the type skull of 

 Triccratops prorsus, which is that of a fully adult though com- 

 paratively small animal, and is thus analogous to that in the 

 skull of the human infant. 



The loss of the frontals and nasals from our specimen 

 renders possible the study of the interior of the skull, the bones 

 of which are admirably preserved, and while the entire skull 

 gives an appearance of massiveness, the individual bones are 

 comparatively thin, but so constructed as to brace in the 

 most admirable manner the portions of the skull subject to 

 strains and impact, especially beneath the horns. 



The frill viewed from above presents much the same relative 

 expanse of bone as is shown in the ventral aspect except that 

 the squamosals now extend forward and upward to the base of 

 the horn cores. Anteriorly they are bounded by the jugals, the 

 infratemporal vacuities, and the quadrates. On one squa- 

 mosal, and to a less extent on the other, a ridge for muscular 

 attachment extends diagonally upward and backward across 

 the posterior portion of the bone. The parietals have the 

 same extent as in the ventral view except that here they 

 overlie the occipital bones and articulate with the postf rontals 

 at about the posterior limit of the horn cores. The supra- 

 temporal vacuities open forward beneath the postfrontals and 

 above the parietals into the main sinuses of the skull. Large 

 blood-vessels had their exit through these vacuities, their 

 branches being deeply impressed into the surface of the parie- 



