AIR-SACKS 5 
are present in great numbers between the muscles and the roots of 
the feathers. These birds when inflated and pricked emit a 
peculiar hissing noise through the skin. It is well known that a 
bird which has its humerus shattered by shot can for some time 
breathe, although its beak and nostrils be tightly closed, and thus 
be submitted to unnecessary excruciating pain. Compression of 
the thorax and abdomen suffocates a wounded bird better than 
strangulation. 
IJ. The naso-pharyngeal or tympanic system of air-sacs is 
restricted to the head, extending chiefly into the occipital, frontal, 
parietal, quadrate,and mandibular bones. To this system belong 
the Eustachian tubes (see EAR and SKULL), the tympanic, and other 
cavities which communicate with the nose. The most curious 
dilatation belonging to this system is the crop-like pouch of the 
ADJUTANT. ‘This sac communicates in Leptoptilus crumenifer with a 
large cavity below the orbit and the pterygoid bone on the left side 
of the basis cranii, opening directly into the nasal cavity and extend- 
ing like a hernia into a loose fold of integument, the pouch being 
divided into two by a vertical membrane which descends to the 
level of the eighth cervical vertebra. 
Another inflatable sac is the gular pouch of BusTarps. It seems 
to be developed only in adult males, reaching its greatest size 
during the breeding season, and again shrivelling up during the rest 
of the year. Its opening is a L-shaped slit in front of the frenulum 
of the tongue and below this organ; the opening can be closed by 
muscles, and leads into a large, glandless blind sac (about 8-10 inches 
long, with half the width), which is a dilatation of the frenulum 
and hangs down between the throat and the skin of the front of 
the neck. It seems to be an entirely sexual ornament, inflating the 
skin, and containing neither water nor food. 
A similar homologous structure exists in the male of Biziura 
lobata, as a little pouch between the two halves of the frenulum, 
with a roundish opening, but apparently not extending into or 
inflating the outer cutaneous wattle or fold underneath the 
mandibles. 
Lastly, the tracheal pouch of the EMeu may be mentioned. It 
is a large unpaired hernia-like sac of the tracheal walls, communi- 
cating with the trachea through a longitudinal slit on the ventral 
side, an individually-varying number of from five to fourteen car- 
tilaginous rings being known to be deficient in the middle line. In 
the embryos this deficiency is already shewn, but the pouch is 
developed much later, and attains its full size in the adults of both 
sexes. This organ seems to act as a resounding bag to the peculiar 
drumming noise made by the adult birds. 
The funetion of all these air-sacs has been the subject of many 
controversies. Some are undoubtedly subservient to sexual orna- 
