xo. 1660. SKULL OF TRrCERATOrS— HAY. 99 



The identification of these bones and foramina may begin with the 

 foramen ovale, that opening through which tlie fifth nerve escapes 

 from the brain cavity. This has been correctly identified by Hatcher." 

 In Cat. Xo. 2-I:l() this foramen has, on the inner surface of the brain- 

 case (Plate 2, fig. 1, J), a diameter of about 12 mm., and it is of a 

 somewhat squarish form. On the outer surface (Plate 1, fig. 1, 5^'^) 

 the diameter is about IG mm. The bone here has a thickness of about 

 28 mm. It may be here remarked that the foramina of this skull 

 are usually really short canals, having inner and outer ends. In the 

 passage for the fifth nerve, not far from its inner end, there is given 

 oil' a large canal wliich is directed forward, emerging on the outer 

 surface of the skull about 30 mm. in front of the foramen ovale (Plate 

 1, fig. 1 J^). Through this canal passed forward the ophthalmic 

 branch of the fifth nerve. Hatcher writes that the anterior opening 

 is the foramen rotundum, and conveyed the maxillary branch ; but the 

 structures here are identical with those in the alligator. Out of the 

 external end of the foramen ovale (Plate 1, fig. 1, 5^' ®) issued the 

 second and the third branches of the fifth nerve. 



Now, the foramen ovale is situated between' the prootic and the ali- 

 sphenoid bones. In the alligator the larger part of it is in the prootic ; 

 and the same is the case in Camptosmirus. Hence, in Triceratops 

 the suture between the prootic and the alisphenoid may be provi- 

 sionally drawn through the front of the foramen, carrying the suture 

 up to the parietal. 



On the inner surface of the brain-case (Plate 2, fig. 1, 6), a little 

 below the foramen ovale, there is seen the posterior orifice of a canal 

 4 mm. in diameter, for the transmission of the sixth nerve, just as may 

 be seen in the alligator. The canal runs the length of the basisphe- 

 noidal bone, emerging at its anterior end. In Hatcher's fig. 8 it is 

 indicated by the letter s and explained as being an undetermined 

 foramen. 



In Hatcher's figure just quoted there is indicated by the letters earn 

 a small fonnmen just behind the foramen ovale. This is explained 

 with a query as being the internal auditory meatus. Being on the 

 outside of the brain-case it can not be that meatus. In fig. 24 the same 

 foramen is said to be the external auditory meatus. The meatus 

 properly so-called is a part of the external ear and this reptile proba- 

 bly had no such organ. The foramen in question is that for the 

 escape of the seventh, or facial, nerve (Plate 1, fig. 1, 7). It has 

 the same position as in the alligator and, as in the latter animal, goes 

 straight through the prootic bone. Outwardly it opens between two 

 descending ridges of bone, which enclose a smooth groove, along 

 which the nerve passed downward. A similar groove is seen in the 

 alligator and in Camptosaurus. 



» The Ceratopsia, p. 17, fig. 8, fo. 



