1896. ] NEW YORK ACADEMY OF SCIENCES. 177 
side and out with a layer of small calcareous plates. The cavity 
within the capsule is known as the capsular or perilymphatic 
cavity, and incloses the internal membranous labyrinth or ear. 
The cavity is an irregular chamber with canals arising from it. 
In the freshly killed animal this cavity contains a thin, trans- 
parent and watery substance, the perilymphatic fluid. There 
may also be seen a network of fine connective tissue fibres which 
connect the membranous portions of the ear with the walls of 
the cavity, holding them in place and at the same time support- 
ing the blood vessels of the ear. Where the membranous parts 
are in close contact with the walls of the cavity the fibres form 
a cushion between the membrane and the wall. These fibres are 
especially distinct in preserved material. 
The internal ear consists of a body made up of two parts 
closely united and three curved tubes that arise from the body 
in different planes. The divisions of this body portion are called 
the sacculus and the utriculus, and the tubes given off, the 
semi-circular canals. The sacculus gives off a small, rounded 
body, the lagena. The recessus utriculus is near the proximal 
end of the utriculus and under the ampulle of the anterior 
and horizontal canals, Figs. 1-5 show these parts as seen from 
the side, back, above, front and behind. The transverse and 
vertical diameters of the ear are approximately equal. The 
axial diameter is somewhat greater. 
Let us now look at each part of the ear separately, beginning 
with the sacculus (s.) and utriculus (u.) as the most prominent 
and as occupying a central position around which the other 
parts are arranged. 
SAccuLus, 
The sacculus (s.) is the largest division of the ear. It lies 
upon the ventral and inner wall of the body part of the cap- 
sular cavity, occupying a little more than one-half the whole 
space. It may be compared in shape to a flattened sack or 
flask, the sides of which project more posteriorly than anteri- 
orly. The upper part of the sacculus is marked by a depression 
that extends somewhat diagonally across the dorsal surface. 
(* * Fig. 5.) The portion above this depression is the utricu- 
lus (u.). If we examine the inner or ventral wall of the sac- 
culus (s.) we find no line of separation. The sacculus seems to 
pass into the ductus endolymphaticus (d. end.), gradually nar- 
rowing down until it becomes a ‘small tube not more than 1 mm. 
in diameter. This tube, which is the ductus endolymphaticus 
proper, passes upward just in front of the connecting tube of 
posterior canal (p.c.t.), inclines a little toward the median 
TRANSACTIONS N. Y. ACAD. Scr., Vol. XV., Sig. 12, August 3, 1896. 
