100 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxvi. 



On the inner surface of the brain-case, behind the foramen just 

 described, is a large oval opening (Plate 2, fig. 1, 10) whose greater 

 axis, 18 mm. long, is directed upward and backward. Hatcher (p. 

 16) has called this the foramen lacerum posterius. It is the common 

 mouth of two short canals which emerge, the one behind the other, 

 on the outer surface of the skull (Plate 1, fig. 1, fen and 10). Be- 

 tween the two exterior openings there is a great ridge of bone 10 

 mm. thick, that ascends from the basioccipital process to the paroc- 

 cipital process of the exoccipital. In the alligator a corresponding 

 ridge forms the lateral boundary of the lower part of the exoccipital, 

 and it is probable that in Triceratops the ridge is on the exoccipital. 

 The anterior of the two exterior openings mentioned is the larger. It 

 is funnel-shaped, the mouth of the funnel having a horizontal diam- 

 eter of about 20 mm. and a vertical diameter of 15 mm. The 

 hinder canal likewise expands as it approaches the surface, and forms 

 a triangular foramen Avhose diameters are about 10 mm. and 15 mm. 

 In the figure referred to last this opening is hidden by the ridge of 

 bone described. The line from 10 is directed to it. 



Hatcher " has identified the anterior of these foramina as the outer 

 end of the foramen lacerum posterius, the hinder as the place of exit 

 of the tenth and eleventh nerves. However, on page 37 he writes 

 that he has interpreted the anterior branch from the internal foramen 

 lacerum j)Osterius as having conveyed the tenth nerve to the brain. 

 He there states further that some anatomists may regard the anterior 

 of the two outer foramina as the external auditory meatus, its internal 

 opening as the internal auditory meatus. 



There is no doubt in the mind of the writer that the anterior of the 

 outer foramina in question is the fenestra ovalis, the opening into the 

 vestibule of the internal ear. In life it was probably partly or 

 Avholly closed by the expanded end of the stapes. So far as known 

 to the writer, this bone has not yet been found in any member of the 

 Ceratopsia. It was quite certainly a long slender rod, which ex- 

 tended from the fenestra ovalis to the outer surface of the»skull, run- 

 ning first below the paroccipital process, then behind the (puidrate, 

 reaching the skin in the notch found in the lower border of the frill. 

 It could hardly have been less than a foot in length. A very similar 

 stapes is found in the alligator and in most other reptiles. 



The hinder of the two external foramina discussed above is the 

 proper foramen lacerum posterius, or jugular foramen (Plate 1, 

 fig. 1, 10), and it transmitted the ninth, tenth, and eleventh nerves 

 of its side, besides also the jugular vein. The foramen credited by 

 Hatcher to the eleventh nerve is the anterior condyloid foramen and 

 probably transmitted a vein. The foramen for the twelfth nerve 

 (Plate 1, fig. 1, 12) is correctly identified. 



" The Ceratopsia, p. 16, fig. 8. 



