The external ear differs considerably in size, thickness, and position.
It may be carried vertically, inclined inward, or hang downward. It is
relatively wide and is little curved except at the base. The concave
surface presents several cutaneous ridges which correspond approximately
with the long axis of the ear. The anterior border of the concha is
strongly recurved in its lower part, and divides into two branches, one
of which passes almost horizontally backward in the cavum conchæ, while
the other continues the general direction of the border. The posterior
border is slightly concave above, strongly convex below, forming a
prominence somewhat analogous to the lobule of the human ear. The
osseous external auditory meatus is very long and is directed downward
and inward. The tympanic membrane is almost circular.
The tympanic cavity proper is small, but it is continuous with the
numerous cells of the large bulla ossea. The Eustachian tube is short;
its pharyngeal opening is situated in the upper part of the wall of the
pharynx immediately behind the posterior nares. It is somewhat
infundibular, and is bounded internally by a thick fold of mucous
membrane (Torus tubarius).