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Show 1867.] DR. J. MURIE ON THE EMU. 411 performs in the animal's economy is inquired into, greater difficulty is found in satisfactorily demonstrating its definite nature and use than in merely describing its structure. Fremery, the original discoverer, supposed the tracheal opening to be in some way connected with the well-developed thoracic air-sacs in this bird, and so to subserve the respiration and sanguification of the blood while running at a high speed. Fig. 2. Portion of thorax and neck of young $ E m u partially dissected, and with the ribs on the left side thrust outwards from the sternum (S) to show the insertion of the sterno-tracheal muscle (S.t.m. S.t.m'.). T.p. Tracheal pouch. • ' * points to the dotted line indicating the tracheal aperture. S. Sternum. 8. t. m. S. t. m. Sterno-tracheal muscles (on the left side the pointer only reaches the thoracic vein instead of the muscle lying beyond). C. a. Carotid artery. C. v. Carotid vein. g. Gland. Pl. m. Platysma myoides. Pn. s. Pneumatic sac. Cl. Cl'. Clavicles. W. W. Wings, cut short. H. s. Hyo-sternal process (Geoff.) (costal process of some writers). Li. Liver. Dr. Knox has very oddly suggested the use of the sac as a swimming- bladder. Alluding to the occasional sudden inundations of the Australian plains and the termination of the rivers in marshes in that country, he says : - " The Emu, forced to seek his food amidst these fens, may, when obliged to have recourse to swimming (which must often be the case), fill the muscular bag of the trachea with air, and thus convert it into a swimming-bladder." He further remarks it may be useful in running; for "by its means and the precaution of shutting the glottis the bird will be enabled to cause the air of one inspiration to pass and repass the |
