PROCEEDINGS OF THE l^ATIONAL MUSEUM 



ATiL. 87 



small foramina that probably carried nutrient blood vessels into the 

 interior of the bones. 



On the ventral side the subtriangular central portion forms the 

 roof over the olfactory part of the brain. The roughened grooves at 

 each side of this central area represent the sutural contacts of the 

 frontals with the underlying ethmoid and orbitosphenoid bones. 



Outside of these sutures the sur- 

 faces are smoothly excavated, 

 forming the roof of the orbital 

 cavities. Measured at the center 

 of the orbital rim the frontals 

 have a greatest width of 77 mm. 

 This part of the skull was ap- 

 parently not recovered with any 

 of the American Museum of 

 Natural History specimens of 

 Leptoceratops, and thus it can- 

 not be contrasted with them. 

 From the frontals of the related 

 Protoceratops these may be dis- 

 tinguished by the greater concav- 

 ity of the dorsal surfaces, rela- 

 tively shorter contribution to the 

 orbital rim, and the more trans- 

 verse direction of the sutural 

 union with the postfrontal. 



The nasals are represented by 

 the greater portion of the left, 

 and a small median part of the 

 right, as shown in figure 2. On 

 the median line they are united 

 by a continuous tongue-and- 

 groove suture, as in Leptocera- 

 tops gracilis Brown. 



The anterior end of the left na- 

 sal is broken off and missing, but 

 sutural surface for articulation with the most of its outcr lateral border is 



prefrontal. One-half natural size. -,■ ^ • 



complete, thus displaying the ex- 

 tent of the sutural contact between it and the ascending process of the 

 premaxillary and with the prefrontal, as indicated in figure 2. 

 Judged from the skull of Protoceratops the lachrymal probably filled 

 the intervening space. The external surface of each nasal bone, 

 more especially the median posterior portions, is roughened and 

 further sculptured by shallow grooves, evidently for the transmission 

 of nutrient blood vessels. These surfaces gave no evidence of the 



FiGUKH 2. — N a s a 1 s of Leptoceratops sp. 

 (U.S.N.M. No. 13864) : Top view, a. An- 

 terior ; p, posterior ; jimx-, sutural surface 

 for articulation with the premaxillary ; prf, 



