‘158 ANTHROPOLOGY. 
membrane and the 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 fibrille of the auditory nerve, and some fine capillary 
vessels. In the postertor 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 ¢nferior 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 aqgueductus vestubuli, which opens in a suture on the posterior 
wall internal to the common opening of the semicircular canal, and trans- 
mits a small vem. In the anterior horn there is a depression (fossa hemi- 
spherica), cribriform, for the passage of nerves. It is separated from another 
cribriform depression (fossa elliptica) by a prominent bony ridge (emimentia 
pyramdalis). 
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. ‘T'wo 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 scalee. 
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 infundibulum. 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 1s 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 hamulus 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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