xo. 1666. OSTEOLOGY OF CAMI'TOSAtJRUS—GILMORE. 217 



their internal openings being 5 mm. apart, the anterior being the 

 smaller and occupying a more ventral position. It was first thought 

 that both of these foramina belonged to the hypoglossal, and I find 

 that Andrews" has so interpreted similarly placed openings in the 

 skull of Igi/anodon, although he suggests that the spinal accessory 

 may have occupied one. Hatcher '' considers that in Triceratops the 

 two posterior foramina transmitted the XII and XI nerves. 



I am inclined to the opinion, however, that the second and more 

 ventrally placed foramen was for a vein, as found in the living 

 crocodile, the first being the true hypoglossal foramen (see XII, 

 fig. 5). A few millimeters anterior to the opening for the twelfth 

 nerve is a third foramen, shown IX and X, fig. 5, which is identified 

 as the foramen lacerum posterius, through which the pneumogastric, 

 vagus, and glossopharyngial nerves were transmitted. This foramen 

 extends forward diagonally through the exoccipital, passing out on 

 its anterior border into a large foramen (see VIII, fig. 5), between 

 the exoccipital, opisthotic, and prootic, just before the latter enters 

 the brain case. Externally the foramen lacerum posterius is sepa- 

 rated from the foramina posteriorly by a weak vertical ridge, and 

 anteriorly by a heavier rounded ridge which rises near the base of 

 the exoccipital and extends diagonally upward and backward, fading 

 out on the lower border of the paraoccipital process. Six millimeters 

 anterior to the foramen lacerum posterius is another small foramen 

 which passes through the antero-external corner of the exoccipital, 

 and also opens into the large foramen mentioned above. Its function, 

 however, is unknown. 



From the position of the large foramen (VIIT, fig. 5), bounded 

 principally by the otic bones, I identify it as the internal auditory 

 meatus, through which the auditory nerve leaves the cranial cavity 

 and enters the internal ear. This interpretation appears to be 

 approximated in the long, slit-like internal auditory meatus in 

 extant Crocodila, which is also bounded by the opisthotic, prootic, 

 and exoccipital. As in the crocodile, there is no ossified division of 

 this opening into the fenestrse ovalis and rotunda. 



Eight millimeters anterior to the internal auditory meatus, a small 

 foramen pierces the median part of the prootic which is considered 

 the exit of the seventh or facical nerve (see VII, fig. 5). Below, a 

 deep, vertical depression leads up to this foramen from the slit- 

 like fissure on the lateral border of the basisphenoid through which 

 the carotid enters the pituitary body. 



Huxley " writes that in all higher Vertebrata " the third division 

 of the trigeminal or fifth nerve always leaves the skull behind the 



"Annals and Magazine of Natural History, 6th ser., XIX, 1897, p. 590. 

 ^-Mon. U. S. Geol. Surv., XLIX, 1907, pp. 36, 37, fig. 31. 

 ^Anatomy of Vertebrated Animals, 1872, p. 70. 



