. Birds: the elements of ornithology . d anAcromyoidal manner, or into their middle parts, a mode whichis distinguished as Mesomyoidal. A condition in which thetrachea alone forms the vocal organ is spoken of as Tracheo-phonal. An arrangement in which the lower end of the tracheais not modified to form a vocal organ is called Oligomyoidal. Parrots have no os transversale or septum dividing the lowerend of the trachea, and they have only three pairs of intrinsic THE EESPIEATOET SYSTEM. 215 muscles. They speak with the aid of their tongue and beakalone. The syrinx may be altogether absent, as in
. Birds: the elements of ornithology . d anAcromyoidal manner, or into their middle parts, a mode whichis distinguished as Mesomyoidal. A condition in which thetrachea alone forms the vocal organ is spoken of as Tracheo-phonal. An arrangement in which the lower end of the tracheais not modified to form a vocal organ is called Oligomyoidal. Parrots have no os transversale or septum dividing the lowerend of the trachea, and they have only three pairs of intrinsic THE EESPIEATOET SYSTEM. 215 muscles. They speak with the aid of their tongue and beakalone. The syrinx may be altogether absent, as in the AmericanVultures and in the Ostrich and its allies. The lunys are two oval flattened organs fixed in and imbeddedbetween the ribs from the second dorsal vertebra to the texture is loose and spongy. The two ^ronehi penetratetheir anterior surface, and divide into four or six branches by side openings on the surface, which openings com-municate with air-sacs, which are usually nine in number. Fig. Diagram of a Lobclh op the Lung op a Eird : greatly magnified(flfter Thomas Williams). Normally one of these is situated between the clavicles, andgives out a process on either side which, passing into the axillaor arm-pit, enters the humerus *. Two others penetratethe abdomen, and often enter the sacral vertebrae and eachfemur; four permeate the more anterior region of the trunk,and two go to the neck. The latter often send branches intothe bodies of the cervical vertebrae. These air-sacs do notsupply air to the cranial bones. These are supplied from thenose and the cavity of the outer part of the ear. * John Hunter tied the windpipe of a fowl and then divided the humerUs,and he found that it breathed through the aperture in that: bone. 2l6 ELEMENTS OP OENITHOLOGY. The bronchi lose their rings after entering the lungs, andgive off secondary branches at right angles (fig. 166), and theseagain tertiary ones in a similar way, ultimately ending, in
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