HEAD. 91 



external cellular, the internal epithelial. 2 — Mem- 

 branous semi-circular canals, corresponding to the 

 osseous canals. 3 — Membranous cochlea, forming 

 three cavities: one inferior tympanic, one superior or 

 vestibular, one middle or auditory, containing the organ 

 of Gos^. € cn^ 



Fluids of labyrinth: that of the membranous laby- 

 rinth, or endolymph ; that of the osseous labyrinth, 

 or peri-lymph. 



Cranium* — Formed by the frontal, parietal, occipi- 

 tal, ethmoid, sphenoid and temporal bones. Division : 

 Four planes and two extremities. Superior plane 

 presents the internal occipital protuberance with its 

 lateral and median crests. Inferior plane, the basilar 

 groove, pituitary fossa, optic fossa, foramen lacerum, 

 cavernous sinuses, maxillary fissures and mastoid fossa. 

 Lateral planes covered with digital impressions. Poste- 

 rior extremity, occiptal foramen. Anterior extremity, 

 the crista-galli process, the ethmoidal fossa and the 

 cribriform plate of the ethmoid. 



It is lined by three meninges : The external or dura 

 MATER, a fibrous membrane forming three folds: the 

 falx cerebri between the cerebral hemispheres, which, in 

 old animals, has as its posterior extremity the Pacchi- 

 onian glands or meningeal granulations ; the tentorium 

 cerebclli between the cerebrum and cerebellum ; the 



