106 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



TOL. 65, 



in figure 4. I can hardly believe, in the light of the Brachyceratops 

 skull, that the postorbital bone has been so reduced in size in Tricera- 

 tops as indicated by Huene. In a recent paper by Lambe ^ the small 

 bones interposed between the prefrontals and identified as the fron- 

 tals represents without question the forward ends of the postfrontals. 

 The frontals, as pointed out by Huene,^ do not appear on the 

 dorsal surface, but are excluded from that view by the overlying pre- 

 frontals (the lachrymals of Huene). Figure 6 shows a longitudinal 

 section of the skull of Triceratops -fiabellatus Marsh after Lull where 



., /Sor. 



.^.«g 



r.of/if /' 



" '/ 



W. 





-M s^i. 



Orbs 



jSec- 



Fig. 3. — Sdperioh view of brain case of Triceratops serratus MabsHj No. 2416, 

 U.S.N.M. Abodt one-third natural size. Al. sp., alisfhenoid ; B. oc, basioc- 

 ciPiTAL ; B. oc. PR.^ basioccipital process ; Ex oc, ExocciPiTAL ; F., showing ex- 

 tent of THE articulation OF THE FRONTAL WITH THE UNDERLTIXG ORBITOSPHEXOIDS ; 



fm., foramen magnum; oc, occipital condyle; o. po., paraoccipital processes; 

 Or. bs., orbitosphenoids ; Sec, line indicating point of separation of two 

 halves of brain case, of which a section is shown in fig. 2 ; s. oc, supba- 

 occipital. 



the frontal = prefrontal + postfrontal) is indicated as having an 

 inferior branch directed downward and backward from the nasals 

 to the anterior part of the brain case. This lower branch represents 

 the true frontal as is clearly shown by the juvenile Brachyceratops ^ 

 skull in which the overlying pre- and postfrontals exist as distinct 

 elements. A study of the sectioned skull (No. 5740, U.S.N.M.) 

 plate 8 and text figure 1 now enables me to definitely determine for 

 the first time the posterior extent of the frontals, as being the thick- 

 ened bone immediately overlying the olfactory lobe of the brain, 



^ Museum Bull. No. 12 Canada Department of Mines, pi. 9, 



»Neues .Tahrbuch, vol. 11, 1012, fig. 1. 



s See Prof. Paper 103, U. S. Geol. Surv., 1917, p. 10, fig. 6. 



1, 2, 1915. 



