. A history of birds . dominal cavity. This elaborate system of air-chambers is further complicated inmany birds by an extensive systemof pneumatic cells extending betweenthe muscles, and between the musclesand the skin, so that the bird is abso-lutely encased in a layer of air en-closed between the skin and thebody. This emphysematous condi-tion is most perfectly developed inbirds such as the Gannets, Screamersand Hornbills. TJie Ncxso-pharyngeal System ofA ir-sacs But there is yet another systemof air-cells to be mentioned, whichis known as the tympanic or naso-pharyngeal system . Whilein th
. A history of birds . dominal cavity. This elaborate system of air-chambers is further complicated inmany birds by an extensive systemof pneumatic cells extending betweenthe muscles, and between the musclesand the skin, so that the bird is abso-lutely encased in a layer of air en-closed between the skin and thebody. This emphysematous condi-tion is most perfectly developed inbirds such as the Gannets, Screamersand Hornbills. TJie Ncxso-pharyngeal System ofA ir-sacs But there is yet another systemof air-cells to be mentioned, whichis known as the tympanic or naso-pharyngeal system . Whilein the majority of birds this is con-cerned merely with the supply of airto the bones of the skull, in theAdjutant Storks it gives rise to avery remarkable pouch which runsdown the front of the neck as faras its middle. It can be inflated anddeflated at pleasure, communicatingas it does with the nasal chamberthrough an aperture in the floor ofthe orbit,-pouches of the Great Bustard and thehere. That of the first-named forms. III. 6.—Dissection ShowingTHE Lungs and Air-sacs ovA Bird Pb. s. = Pre-bronchial = Axillary sac bounded ex-ternally by the breast-muscles,seen here in section. S. s. =Partition dividing anterior inter-mediate sac () from thesub-bronchial sac. = Pos-terior intermediate sac. =Oblique septum. = Hori-zontal septum. L. Ab. s. =Left abdominal sac. H. =Heart. G. = Gizzard. L. =Liver. In. = Intestine. (AfterStrasser.) The extraordinary airEmu may be mentioned INTRODUCTORY 19 a relatively enormous cavity, having extremely thin walls, lyingimmediately under the skin of the neck, and opening im-mediately under the tongue. Peculiar to the male, it must beregarded as a variation of the pouch described just now in theAdjutant. Only one other bird possesses a similar chamber, andthis is the Musk Duck {Biziura lobatd). But here the pouch isvery small, and is lodged in a sac depending from the under-side of the lower jaw. The pouch of the Emu is
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbirds, bookyear1910
