TIIK RAB15IT. 273 



occipital below : the tympanic is closely applied to its outer 

 surface, the tympanic cavity being enclosed between the 

 two bones : a process from its posterior edge fits over the 

 groove just noticed in the tympanic, completing the stylo- 

 mastoid foramen and helping to keep the two bones in 

 position. On its outer surface, and therefore seen only 

 when the tympanic is removed, are two small apertures, the 

 anterior of which is the fenestra rotunda, the posterior 

 the fenestra ovalis. On its inner or cranial surface 

 is a large hemispherical depression, the floccular fossa, 

 for the lodgment of the flocculus of the cerebellum ( 477), 

 and beneath this is a shallow depression, the internal 

 auditory meatus, with two apertures in it for the trans- 

 mission of the seventh and eighth nerves (491, 492). 



57. The foramen lacerum medium : a large space 

 between the periotic and alisphenoid : it transmits the third 

 division of the fifth nerve ( 357). 



58. The foramen lacerum posterius : a space 

 between the periotic and the exoccipital, through which the 

 ninth, tenth, and eleventh nerves leave the skull ( 493). 



59. The mesethmoid : this is seen only in the dis- 

 articulated or bisected skull : it consists of two parts, the 

 cribriform plate, riddled with numerous small holes for 

 the passage of the olfactory nerves, and completing the 

 antero-inferior portion of the wall of the brain-case, and 

 of the lamina perpendicularis, a median vertical plate, 

 which proceeds from the anterior surface of the cribriform 

 plate into the nasal cavity. In the recent state the lamina 

 perpendicularis is continued forwards by a cartilaginous 

 plate, the septum nasi, and the two together separate the 

 right and left nasal cavities from one another. 



60. Lying against the ventral border of the septum nasi are the 

 paired scroll-like Jacobson's cartilages : they are attached in 



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