The Ear
There is no auricle; the external ear consists only of the external acoustic meatus, which opens on the side of the head under cover of a patch of small feathers. The meatus is short and straight, so the relatively large tympanic membrane can easily be examined (and as easily injured).
A lobe, similar in structure to the comb and wattle, is present ventral to the opening (Fig. 37.1/4). Among domestic chickens, the color of the earlobe matches the color of the shell of the eggs the hen lays.The middle ear resembles that of mammals, except for the modification of the ossicles. The tympanic membrane is connected to the vestibule window by the columella and the homologue of the mammalian stapes, a tiny osseous rod expanded at each end.
The structure and subdivision of the inner ear follow the mammalian pattern. The cochlea does not form a spiral and is only slightly curved, although it is significantly shorter than its mammalian counterpart; a relatively thick layer of sensory cells seems to compensate for brevity.
Comprehension Check
Because of the importance of the following in poultry diseases, review the structure of the following organs: lungs, heart, kidneys, liver, and lymphoid organs.
Of the 27 orders among which birds are divided, those likely to be of the most frequent veterinary concern are Galliformes, Anseriformes, Columbiformes, Psittaciformes, Falconiformes, and Passeriformes—or, in more familiar terms, the domestic chicken and its relatives, ducks and geese, pigeons, parrots and budgerigars, hawks and eagles, and the so-called songbirds, respectively. This list is less limited than it might initially appear because, by itself, the Passeriformes order includes some 5700 of the nearly 9700 species of birds currently recognized.