7
THE LABYRINTH
0. LOWENSTEIN
I. Structure
. . .
A. Semicircular Canals
B. Otolith Organs . .
C. The Sensory Hair Cell
11. Function
. . .
A. Equilibrium
. .
B. Hearing
. . .
References . . . .
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. . . . . . . . . 2 1 1
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I. STRUCTURE
The labyrinth is considered to represent the final stage in the process
of submergence of neuromast organs of the lateral line type, and it has
become completely or, at any rate, almost completely, separated from
the outside medium and enclosed in the brain case. The “duct’us endolymphaticus” maintains a tenuous connection with the outside world in
the elasmobranchs only. The labyrinth originates ontogenetically from a
common placode with the lateral line. Wilson and Mattocks (1897) described the early states in the formation of a common rudiment ( Anlage)
in the early salmon embryo. On about the twelfth day, the “embryionic
shield thickens into a neural keel. Immediately at each side of this is
left a comparatively thick streak of ectoderm which extends through the
anterior two thirds of the embryo. It is the lateral sensory rudiment.
Toward the end of the thirteenth day the middle portion of the rudiment
begins to be invaginated to form the auditory sac. The auditory sac comes
thus to lie between a preauditory and a postauditory rod of cells which
give rise to the infra- and supraorbital canals of the head and to the
lateral line of the trunk, respectively.
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