1808.] DR. J. MURTE ON THE GTJLAR POUCH OF OTIS. 4/7 



pressed at the will of the bird, as evidently is the case in the organ 

 in question. Besides this, the sac presents a wide external aperture 

 (?'. e. into the mouth) with natural and healthy-looking walls lined 

 with mucous membrane. As has been demonstrated, the enlarged 

 tracheal pouch of the Emu is not a sudden or accidental circum- 

 stance, but the further devel >pment of a rudimentary structure 

 found in the young ; so in an analogical manner should we expect to 

 find rudiments of the gular pouch in the young male Bustard. If 

 the gular pouch is, so to speak, sporadic, irregularly dispersed 

 among individual specimens, merely the product of inconstant for- 

 tuitous circumstances, and produced in old birds in what must seem 

 an incredibly short space of time, then in it we have a most extra- 

 ordinary physiological fact, and such as does not tally with our pre- 

 sent knowledge of the laws of development. 



7. Observations respecting the development of this appendage, 

 and especially such as point out the precise period and manner of 

 growth, are yet a desideratum. As I have already hinted in my 

 introductory remarks, some anomalies are certainly difficult of expla- 

 nation. 



8. Finally, with regard to the mechanism of inflation, the first 

 thing is how the air gets there. Now, according to the laws of 

 pneumatics applied physiologically, the pressure of the surrounding 

 atmosphere ordinarily would not be sufficient to overcome the re- 

 sistance and tonicity of the living tissues, such as to produce com- 

 plete distention. Neither is it likely that sufflation is the result of 

 a vacuum. A lengthened inspiration may aid, but I believe cannot 

 directly and fully dilate the cavity ; that is to say, the tongue 

 being raised and the aperture into the gular pouch unobstructed, 

 the air drawn into the lungs during the inspiratory effort would not 

 equally rush in and fill the gular sac to repletion, as necessarily it 

 does the pulmonary cells and pneumatic cavities. The lungs and 

 subsidiary air-passages once full, however, and expiration naturally 

 taking place, the mouth and posterior nasal passages require only to 

 be partially closed for the thoracic muscular contraction to drive the 

 air into the sac. In other words, muscular power is as requisite to 

 inflate it as to empty it. A familiar illustration might be given in 

 the blowing out of a bladder. Judging from the actions of the living 

 Australian Bustard, the above explanation holds good, inasmuch 

 as previous to expansion of the gular pouch it does not gape, but 

 inspires quietly. When the pouch is blown out and the bird utters 

 the cooing snapping sounds, the mouth is then more or less open. 

 The cooing noise may be laryngeal. If from the gular pouch, com- 

 pression of the muscular and fibro-elastic tissues of the neck must 

 drive the air out, which, the fibres at the neck of tbe sac resisting, 

 cause it to escape in jets. By relaxation of the mandibular fibres 

 and contraction of those of the inferior part of the neck, emptiness 

 of the pouch results, and the neck assumes its usual proportions. 



