7 
724 THE ORGANS OF SENSE. 
Corti (Fig. 530). 1t consists of bipolar nerve-cells, and each nerve fibre, probably, has 
its continuity interrupted by one of these cells. Beyond the ganglion spirale the nerve 
Nerve fibres which pass out fibres extend outwards,at first in bundles, 
between the two layers of the and then in a more or less continuous 
Spiral fibres lamina spiralis ossea 5 7 on 
sheet, from the outer edge of which they 
are again collected into bundles, which 
pass through the foramina nervosa of the 
labium tympanicum. Beyond this they 
appear as naked axis-cylinders, and, 
turning in a spiral manner (inner or first 
spiral fasciculus), send fibrillee towards 
the inner row of hair cells. Other fibrils 
pass outwards between the inner rods 
and form a second spiral fasciculus in 
Corti’s tunnel, from which fibrils extend 
outwards across the tunnel, and, passing 
between the outer rods, enter Nuel’s 
space. They form a spiral fasciculus on the inner aspect of each row of Deiters’ cells, 
and from these fasciculi fibrillee pass towards the bases of the outer hair cells. 
Ganglion spirale 
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Fia. 530.—Part or CocHLeaR NERVE, highly 
magnified (Henle). 
Schwalbe divides the auditory nerve into three portions, viz. : (1) ramus utriculo-ampullaris, 
corresponding with the ramus vestibularis already described ; (2) ramus sacculo-ampullaris, for 
the saccule and posterior ampulla ; and (3) ramus cochlearis, for the ductus cochlearis. 
Vessels of the Internal Ear.—The auditory artery, a branch of the basilar, enters the internal 
auditory meatus and divides into vestibular and cochlear branches. The vestibular branch sup- 
plies the soft tissues in the vestibule and semicircular canals, each canal receiving two arteries, 
which, starting from opposite extremities of the canal, anastomose on the summit of the arch. 
The cochlear branch divides into numerous twigs, which enter the foramina in the tractus 
spiralis foraminosus and run outwards in the lamina spiralis ossea to reach the soft structures ; 
the largest of these arteries runs in the canalis centralis. The stylo-mastoid artery also supphes 
some minute branches to the cochlea. Siebenmann describes the auditory artery as dividing into 
three branches, viz.: (1) anterior vestibular, (2) cochlear proper, and (8) vestibulo-cochlear. The 
veins from the cochlea and vestibule unite at the bottom of the meatus with the veins from the 
semicircular canals to form the internal auditory vein, which may either open into the posterior 
part of the inferior petrosal sinus or into the lateral sinus. Small veins also pass through the 
aqueductus coch- 
lew and aque- 
ductus vestibuly, / Auditory pit 
the former open- 
ing into the in- / 
ferior petrosal 
sinus or into the 
internal jugular 
vein, the latter 
into the superior 
petrosal sinus. 
/ Recessus labyrinthi~ 
/Cavity of hind brain eA 
/ Semicireular canal _ 
DEVELOPMENT 
OF LABYRINTH. 
The epithelial 
lining of the 
labyrinth is de- 
rived from an in- 
vagination of the 
cephalic ecto- 
derm, termed 
the auditory pit, 
which appears ia es Aid): ; we 
at t] In A the epiblast is invaginated to form the auditory pit; in B the auditory pit is closed 
OPE es} e The and detached from the epiblast, forming the otic vesicie ; while C shows a further 
hind brain im- stage in the development of the vesicle. 
mediately above 
the first visceral cleft. The mouth of the pit is closed by the growing together of its 
margins, and it then assumes the form of a hollow vesicle, the otic vesicle, lined by 
epithelium ; the vesicle sinks into the subjacent mesoderm and is met by the auditory 
Fic. 531.—SecTIONS THROUGH THE REGION OF THE HIND BRAIN OF Fa@raL RaBBITs 
(to illustrate the development of the labyrinthine epithelium). 
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