e 
422 SENSE-ORGANS AND INTEGUMENT. 
These two bundles are distinct except at their origin, and 
are sometimes considered as separate muscles. 
Relations. —Outer surface with the tragicus lateralis (4) and 
the fat about the concha. Inner surface with the concha. 
Action.—Flexes the concha. 
Strauss-Durckheim describes under the name cornetocon- 
chzus a small muscle bridging the deep groove caused by the 
folding of the medial surface of the concha, its proximal end 
being close to the insertion of the abductor auris brevis (page 
100). This muscle was absent in all of the cases examined for 
its presence. 
M,. concheus externus (Fig. 169, 9).—A quadrilateral 
muscle on the lateral surface of the concha. The cranial end 
of this muscle is attached to the concha a short distance distad 
of the antitragus along a dorsoventral line six to eight milli- 
meters in length; the fibres pass thence caudodorsad a distance 
of about one centimeter, where they are again attached to the 
concha. The muscle thus bridges a shallow depression on the 
lateral surface of the concha. 
Action. — Constricts the concha. 
The Middle Ear. 
The middle ear is enclosed in a 
cavity within the tympanic bulla. 
Its outer boundary, as well as the 
inner boundary of the external ear, 
Fic. 170, TYMPANIC MEMBRANE, is formed by the tympanic mem- 
VIEWED FROM THE INNER SIDE. brane (Fig. 170, ¢.) This is a thin, 
The outer wall of the bulla has 
been removed, carrying with it the 
tympanic membrane with the mal- 
leus and incus; these are now 
viewed from the side that was 
turned toward the cavity. «, bony 
ring forming inner end of external 
auditory meatus; 4, 4’, malleus; c, 
tympanic membrane; d, incus; ¢; 
lenticular process; 7, chorda tym- 
pani nerve; g, cartilaginous sup- 
port for chorda tympani nerve. 
the membrane gives it the 
face. 
semitransparent membrane attached 
to the bony ring (a) surrounding the 
inner end of the external auditory 
meatus. It is oval in outline. Across 
the dorsal third of its inner surface 
runs the handle of the malleus (0), 
to which the membrane is firmly 
attached and which by pulling on 
form of a cone instead of a flat sur- 
The apex of the cone is directed mediad. 
The middle ear, or cavum tympani, is an ellipsoidal cavity 
