1903.] Lull, .Skull of Triceratops Serratus. 69 1 



wide free margin sheathed with horn as in the frill of Tri- 

 ceratops prorsus} 



The squamoso-parietal suture is a squamous one for a short 

 distance backward, the squamosal overlapping; but at the 

 point where the suture bends outward it becomes a plain 

 harmonic suture having but little strength, as is evidenced 

 by the fact that in the specimen under consideration the 

 squamosal bone had slipped dorsally past the parietal on the 

 right side, while on the left the bones were flush with each 

 other. In the type specimen of Triceratops serratus in the 

 Yale University Museum both sutures, that on the left as well 

 as on the right, have slipped. The frill thus seems to have 

 afforded leverage to assist in moving and supporting the huge 

 head with its weighty armament and also to have protected 

 the neck against the assaults of enemies, but it seems hardly 

 probable in the present species that the dorsal part could have 

 withstood crushing blows without injury to the frill. The 

 hinder margins of the parietals have decomposed somewhat 

 and the marginal ossicles are here wanting, though most of 

 them are present on the squamosals. 



Dorsal Aspect. 



The anterior part of the skull has been weathered oft", as it 

 formed the outcrop of the specimen, and much of the bone has 

 been disrupted by grass roots even where it had not yet been 

 exposed by erosion. 



The postfrontals , with the exception of the horn cores, are 

 entire and the underlying sinus is readily explored through the 

 large postfrontal fontanelle (the parietal or pineal foramen of 

 authors). This sinus is continuous with those of the horn 

 cores and in turn with the space within the skull behind the 

 orbits, but not with the brain case. It is more or less wedge- 

 shaped, tapering dorso-ventrally as one goes forward, the 

 anterior limit being just in front of the orbit. The flat roof is 

 formed by the overlying postfrontal and frontal bones, while 

 the sinus is laterally constricted into three chambers. The 

 anterior chamber has a rather flat floor and is separated from 



Marsh, O. C. 1896. Dinosaurs of North America, pi. Ix, fig. 4. 



