180 EAR 
Birds possess one muscle belonging to the middle ear; this 
muscle acts as a tensor tympani; it arises near the occipital con- 
dyle, passes through a hole into the tympanic cavity, attaches its 
tendon to the ends of the columellar processes, and also spreads 
over the tympanum itself. 
The whole columella of Birds is equivalent to the chain of ear- 
ossicles of Mammals, the inner end of the columellar rod repre- 
senting the stapes, while the outer and lower processes of the 
tympanic end correspond with the manubrium and the long process 
of the Mammalian malleus. The quadrate bone, so well developed, 
and functional as the hinge of the masticatory apparatus in Reptiles 
and Birds, has in Mammals lost this function, and in them is 
reduced and modified into the comparatively insignificant tympanic 
ring, acting only as a frame for the tympanic membrane. 
The inner ear is the most important portion of the whole ear, 
because it contains the sound-perceiving apparatus. It consists of 
the labyrinth or membranous capsule which encloses the end-organs 
of the auditory nerve, and of the cartilaginous or osseous capsule 
which surrounds and protects the membranous organs. The outer 
capsule is consequently more or less a cast of the other, and repeats 
all its principal complicated configurations. 
The membranous ear is a system of hollow tubes which form 
various labyrinthic dilatations and canals, all of which communicate 
with each other. The whole is divided into—I. pars superior, 
consisting of an utriculus, two sinus, three ampulle, and three semi- 
circular canals; each canal connects one ampulla with one of the 
two sinus; the anterior canal runs in a vertical and longitudinal 
plane, the posterior canal lies in a transverse vertical plane, extend- 
ing from right to left, while the external canal stretches out in 
a nearly horizontal direction; II. pars inferior, consisting of the 
cochlea and the sacculus with the endolymphatic duct. The sac- 
culus is a small dilatation or appendix of the utriculus; its walls 
are continued as the endolymphatic duct straight into the cranial 
cavity, ending in the dura mater in the shape of a flattened sac. 
This peculiar arrangement is an imperfect remnant of previous con- 
ditions ; because in Selachians the endolymphatic duct of each ear 
opens upon the top of the head, through the skin, and indicates the 
way by which the primitive ear-capsule (itself, like all the higher 
sense-organs, a modification of epidermal and neural cells) has 
gradually become transferred into the depth of the skull. 
The cochlea ends blindly, with its apex towards the occipital 
condyle; instead of being curled into several turns as in Mammals, 
it forms in Birds never more than, and often much less than, 
half a twist. Its internal structure is most complicated and 
intimately connected with the perception of sound, through the 
possession of “Reissner’s membrane” and the “organ of Corti.” 
