64 : 
ON THE PHYSIOGNOMY OF SERPENTS. 
der or sac without cells, simply formed by a prolongation 
of the serous membrane enveloping the lung ; and, second, 
because the most considerable branches of the air-tubes 
open into this cavity of the lung. By this first arrange- 
ment, the lung of the Ophidians becomes a reservoir so 
spacious as to contain a volume of air, equivalent to a great 
number of inspirations ; by the second, the air contained 
in this reservoir can be forced into the cells by the con- 
tractions of the thorax, without the necessity of a fresh in- 
spiration. 
The figure of the lung undergoes numerous modifications 
in the different species of Ophidians. The form of that or- 
gan is generally that of a simple sac, conical, and extend- 
ing from the heart towards the lower region of the stomach, 
where it terminates in a membranous pouch. The trachea, 
consisting of a great number of semi-annular cartilages 
united anteriorly by a membrane, ends in the upper part of 
the lung by an oblique opening ; this organ divides into two 
branches in the Boa, in most of the genus Tortrix, the 
Dipsas, and several other Ophidians, where we find a vestige 
of a second pulmonary lobule, sometimes about half the size 
of that on the other side. The air-cells of the pulmonary cavity 
of other Ophidians extend on the membrane which unites the 
rings of the trachea, so that they sometimes occupy this mem- 
brane through all its length. There are other species in which 
that membrane is much dilated, and incloses a number of 
air-cells, as considerable as the lung itself. In the Xenodon 
severus, in the true poisonous snakes, and in some other 
Ophidians, this membrane enlarges into a capacious sac, 
which alone contains all the air-cells ; so that from this 
peculiar disposition, we find the lung displaced completely 
by this organ, which, contrary to what we observe in other 
Ophidians, is situated in the fore-part of the neck, between 
the glottis and the heart. The position of the organs of 
respiration in sea-serpents is still more extraordinary. In the 
Hydrophis colubrina the trachea is prolonged to the hypo- 
chondria, where it terminates in a membranous sac, which 
extends to within two inches of the anus ; but, instead of 
a membrane uniting the tracheal rings, it is the lung which 
invests it through its whole length. In the Hydrophis pe- 
lamis, the trachea, dilated at its origin and contracted to- 
