158 ANTHROPOLOGY. 



membrane and tlie base of the stapes. The inner or cerebral wall of the 

 vestibule corresponds with the base of the meatus internus. It is cribriform, 

 and transmits some fibrill£e of the auditory nerve, and some fine capillary 

 vessels. In the posterior and lower horn are seen three distinct foramina, the 

 orifices of the semicircular canals. In the superior cornu are the two other 

 openings of these tubes. In the inferior and anterior cornu is a distinct oval 

 opening, which leads downwards and forwards into the vestibular scala of 

 the cochlea. Thus there are seven large foramina in the vestibule. The 

 smaller foramina are : 1, those in the cribriform lamina for the auditory 

 nerves ; 2, the aqueductus vestibtdi, which opens in a suture on the posterior 

 wall internal to the common opening of the semicircular canal, and trans- 

 mits a small vein. In the anterior horn there is a depression {fossa hemi- 

 sjiherica)^ cribriform, for the passage of nerves. It is separated from another 

 cribriform depression {fossa elliptica) by a prominent bony ridge {eminentia 

 pyramidalis). 



3. Semicircular Canals are three long tubes imbedded in the petrous 

 bone, behind the vestibule, and communicating with it. They are curved 

 so as to form nearly three fourths of a circle. They open by each extre- 

 mity into the vestibule ; two, however, unite by their adjoining extremities, 

 so that but five openings are presented. Two of these canals have a per- 

 pendicular, and one a horizontal direction. 



4. The Cochlea is the most anterior part of the labyrinth, and is a very 

 complicated apparatus. It derives its name from a strong resemblance to 

 the shell of a snail. It may be considered as a tapering tube, closed at its 

 smaller extremity, coiled round a central pillar, the tube itself being sub- 

 divided by a partition into two semi-cylindrical tubes. It presents for no- 

 tice, the tube, the lamina spiralis, the axis or modiolus, and the scalae. 



The tube is about an inch and a half long, and descends two turns and a 

 half. The second turn lies, at its beginning, within the first, but near its end 

 rises above it. The axis or modiolus is a conical tube, whose summit is ex- 

 panded like a funnel.' It arises from the base of the cochlea, and is directed 

 almost horizontally outwards : the coils of the cochlea and of the lamina 

 spinalis twine round it. The whole of this axis is concealed by the tube 

 of the cochlea ; its base or origin is pierced with foramina for the auditory 

 nerves. The apex is expanded into the infundihulum. The centre of the 

 modiolus is traversed by canals for branches of the auditory nerves and 

 blood-vessels. 



The lamina spiralis is a very thin plate of bone wound spirally, like the 

 turns of a screw, round the modiolus, into which its inner margin is insert- 

 ed. In the dry bone, the outer margin is free, but in the recent state it is 

 continued by membrane to the opposite and outer walls of the tube. If 

 unwound and separated from the modiolus, it would present the appearance 

 of an elongated isosceles triangle. The apex of this stands out from the 

 modiolus in the form of a hook {the hamidus of the lamina spiralis). The 

 lamina is composed of two thin plates, between which the cochlear vessels 

 and nerves are distributed. 



The two secondary cavities into which the cochlear tube is divided by 

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