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 sanguifica- 

 tion of the blood while running at a high speed. 



Fig. 2. 



Portion of thorax and neck of young ^ Emu partially dissected, and with the ribs 

 on the lelt 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. 

 S.f.m. S.t.Jn. 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. ff. Gland. PL m. Platysma myoides. P»z. s. 

 Pneumatic sac. 67. CI'. 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 swim- 

 ming-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 



