NO. IGGO. SKULL OF TRICERATOrti— HAY. XQS 



On the lower surface of that bone Avhich the writer regards as the 

 sui^raoccipital (Phite 2, fig. 1, soc), near its anterior end, apparently 

 between it and the parietal, and placed right and left of the mid- 

 line, are found two deep excavations. The mouth of each of these 

 measures about 20 mm. fore and aft and about 15 mm. transversely. 

 The depth amounts to 15 mm. The diameters diminish toward the 

 upper ends of the excavations. The one on the left side (Plate 2, 

 fig. 1, eeh. f) appears to have reached the external surface of the 

 bone, forming a foramen. Whether the one on the other side reached 

 the surface is uncertain, on account of some crushing. Into these 

 excavations there penetrated probably portions of the brain. These 

 will be considered below. 



Xear the upper border of each orbitosphenoid there is found 

 another excavation similar to those just described, having a some- 

 what larger base, but not entering so deeply into the bone. The 

 base measures 20 mm. fore and aft and 15 mm. transversely. From 

 the front of each excavation a foramen (Plate 2, fig. 1, r) pierces 

 the bone, as already mentioned. 



Professor Marsh " published a figure of a cast of the brain-case of 

 the specimen here described. This has been reproduced by Hatcher.'' 

 This figure represents a side view of the brain. Another figure giv- 

 ing a view of the lower surface of the brain of this specimen is pub- 

 lished b}^ Hatcher,'" In that figure the letters VIII on the left side 

 ought to be changed to VII; VIII should be connected with the 

 anterior part of the mass indicated by X; and XI ought to be erased. 



In order to rej^resent more accurately the brain of this specimen, 

 a new^ cast has been prepared by jNIr. William Palmer, of the National 

 Museum, under the superintendence of Mr. Gilmore and the writer. 

 The parts of this brain, as represented by the cast, are indicated in 

 the legend affixed to each figure of Plate 3. Attention must be 

 specially called to certain structures found on the upper surface and 

 which filled the excavations already mentioned. The hinder pair 

 of these is shown on Plate 3, figs. 1, 3, ceh, p. These bodies are 

 near the boundary between the cerebellum and the optic lobes. They 

 are probably parts of the former. Andrews '' interprets a strong 

 development of brain substance in the same region in Iguanodon as 

 the cerebellum ; but that development formed a conspicuous band 

 which culminated in the midline above. In Triceratops the lateral 

 masses are far removed from each other. Marsh's figure of the brain 

 does not adequately rei^resent these masses. 



On the. upper surface of the anterior end of the brain there is seen 

 another pair of processes (Plate 3, fig. 1, 3 cet\ h), not rising, 



°Dlnos;nu"s of North America, pi. lxxvii. fig. 4. 



^ The Ceratopsla, p. .39. 



c Idem, p. 37, fig. 32. 



<'Ami. Mag. Nat. Hist,, 6th ser,, XIX, p, 587, pi, xvi. 



