THE SKULL. 



37 



as 



posterior branch of the more anterior of the two foramina that enter the skull behind and 



at the bases of the basioccipital and exoccipital processes, the anterior branch of which 



previously stated," enters the foramen lacerum posterius just 



before the latter enters the brain cavity. This anterior branch 



I have interpreted as having conveyed the tenth nerve to the 



brain by way of the foramen lacerum posterius. The foramen 



lacerum posterius is the large oval foramen which enters the 



brain cavity just in advance of and below the small foramen 



mentioned above and shown &tflp, figs. 8 and 31. A little 



way within the body of cranial wall this foramen branches, so 



that it has two external exits — one, the larger, in front of the 



basioccipital and exoccipital, the other, the smaller, having 



been already mentioned as opening behind the processes of 



these bones. By some anatomists this foramen, which I have 



interpreted as the foramen lacerum posterius, may be con- 

 sidered as the auditory, and its external and internal openings 



as the external and internal auditory meati. Just in front of 



this large foramen is a small one, earn, fig. 32, piercing the 



heavy bar of bone separating the former from the inner opening 



of the large foramen ovale. This small foramen I have inter- 

 preted as the in- 

 ter nal auditory 

 meatus, though I 

 am by no means 

 sure that it func- 

 tioned as such. It 

 seems, however, 

 at one time to 

 have communi- 

 cated with three 

 small cavities 

 (in, fig. 31) situ- 

 ated within the 

 bony mass oppo- 

 site the constric- 

 tion which marks 

 the division of 

 this portion of 



the brain cavity into posterior and median cere- 

 bral vesicles, while its external opening appears 

 to have been that which I have considered the 

 external auditory meatus . Immediately anterior 

 to this small foramen is the foramen ovale, seen 

 at fo, figs. 8 and 32. This is a very large foramen, 

 equaling in size the foramen lacerum posterius. 

 On its anterior border midway between its exter- 

 nal and internal openings it receives the posterior 

 opening of the alisphenoid canal, which is likewise 

 of considerable dimensions. Some distance in ad- 

 vance of the inner opening of the foramen ovale 



the sphenoidal fissure, seen at sf, figs. 8, 31, and 32, enters the brain cavity just above and at 



the side of the entrance to the deep pituitar}^ fossa. A little in advance of this fissure is the 



Fig. 32. — Inferior view of brain cast of Tri- 

 ceratops serratus, from No. 2065, U. S. 

 National Museum, mo, Medulla oblon- 

 gata; i-xn, cranial nerves; flp, foramen 

 lacerum posterius; cam, internal audi- 

 tory meatus?; fo, foramen ovale; ca, 

 carotid artery; pi, pituitary lobe; pf r 

 foramen entering anterior extremity of 

 pituitary fossa; sf, sphenoidal fissure; 

 ff. undetermined foramina; of, optic 

 foramen; ol. olfactory lobe. One-half 

 natural size. 



Fig. 31- — Horizontal section of brain case of Triceratops flabcl- 

 latus (type) in the plane of the long axis of the brain, No. 

 1821, Yale Museum, oc, Occipital condyle; exo, exoccipital 

 processes; xn, foramen for exit of twelfth nerve; xi, fora- 

 men for exit of eleventh nerve; ftp, internal opening of 

 foramen lacerum posterius; fpf, foramen leading to pitui- 

 tary fossa; sf, sphenoidal fissure; of, optic foramen; ol, olfac- 

 tory lobe; on, exit for olfactory nerves; in, auditory cavities 

 in ? auditory capsules; c, constriction between cerebrum and 

 cerebellum. One-fourth natural size. 



a See p. 10. 



