i8o 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 rej^re- 

 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 ampullae, 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 apj)endix of the utriculus ; its Avails 

 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 ei^idermal 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." 



