840 
ZOOLOGY. 
In the frogs, lizards, and serpents, the lung consists of a 
cavity, the sides of which are cellular. The lower, or poste¬ 
rior part of the organ, either forms a mere membranous hag 
(the parietes of which are not cellular), or else the vesicles 
are larger at that part than elsewhere. In the serpents the 
lung has that elongated form, which characterizes all the 
viscera of these animals. A considerable portion of it is a 
simple membranous cavity; and this is supplied with arteries 
from the surrounding trunks. The turtles have a more com¬ 
plicated structure, or one which approaches more nearly to 
that of the 'warm-blooded classes. The lungs are uniform in 
their texture throughout, but the vesicles are very large. 
The cartilaginous annuli of the bronchi terminate before 
these vessels enter the lungs 
There are numerous projecting processes in the lungs of 
the chameleon and newt; in the latter animal they terminate 
behind in an elongated bladder. The serpents, at least for 
the most part, have only a single lung, which forms an elon¬ 
gated vesicular bag. In a coluber of four feet and a half 
long, the lung measured one foot one inch; its anterior half 
resembled a muscular intestine in appearance, and had an 
elegantly reticulated internal surface, which resembled on a 
small scale the inner surface of the second stomach of the 
ruminating animals. The posterior part formed merely a 
simple and long cavity with thin sides. 
In the tadpole, and the young of such lizards as bring 
forth in water, there are two organs, which somewhat re¬ 
semble the gills of a fish (appendices fimbriatae, Swammer¬ 
dam). These appendices are connected to the sides of the 
neck, and hang loose from the animal; they are not perma¬ 
nent, but are gradually withdrawn into the chest, (within a 
few days, in the reptiles of Germany), where their remains 
may still be perceived for some time near to the true lungs. 
That doubtful animal, the siren lacertina from Carolina, has, 
according to Hunter’s dissection, two bladder-like lungs, 
besides the external branchiae. 
The same circumstance holds good respecting that no less 
mysterious creature, the proteus anguinus, from the Cirknitz 
or Sitticher lake of Carniola; whose remarkable internal 
structure has been described and delineated by Dr. Schreibers 
in the Philos. Trans, for 1801; and more recently by Signors 
Configliachi and Rusconi in their elaborate monograph on 
the proteus anguinus. 
The lungs of birds are comparatively small, flattened, and 
adherent above to the chest, where they seem to be placed in 
the intervals of the ribs : they are only covered by the pleura 
on their under surface, so that they are in fact on the outside 
of the cavity of the chest, if we consider that cavity as being 
defined by the pleura. The cartilaginous annuli of the tra¬ 
chea, which are in general more complete in the other mam¬ 
malia than in man, are perfect circles in birds, and overlap 
each other at their upper and lower margins. Hence the di¬ 
ameter of this part is not affected by any twisting motion of 
the neck. A great part of the thorax, as well as the abdo¬ 
men, is occupied by the membranous air-cells, into which 
the lungs open by considerable apertures. Those of the tho¬ 
rax are divided, at least in the larger birds, by membranous 
transverse septa into smaller portions, each of which, as well 
as the abdominal cells, has a particular opening of commu¬ 
nication with the air-cells of the lungs, and consequently 
with the trachea. The membranes of these cells in the 
larger birds are provided here and there with considerable 
fasciculi of muscular fibres, which have been regarded as a 
substitute for the diaphragm, which is wanting in this class 
of animals. They also serve very piincipally, as we may 
ascertain by examining large birds in a living state, to drive 
back again into the lungs the air which they received in in¬ 
spiration, whence the repletion and depletion of the thoracic 
cells must alternate with those of the abdominal cavities. 
Besides these cells, a considerable portion of the skeleton 
is formed into receptacles for air in most birds; for there are 
indeed exceptions and considerable variations in the different 
genera and species. This structure is particularly marked in 
the larger cylindrical bones, as the scapula, clavicle, and 
femur. It is also found in most of the broad and multan¬ 
gular bones of the trunk, as the sternum, ossa innominata, 
dorsal vertebrae, &c. All these are destitute of marrow in 
the adult bird, at least in their middle; so that the cylin¬ 
drical bones form large tubes, which are only interrupted 
towards the extremities by a sort of transverse bony fibres; 
the broad bones are filled with a reticulated bony texture, 
the cells of which are empty. They have considerable aper¬ 
tures (most easily shewn in those extremities of the cylin¬ 
drical bones which are turned towards the sternum) commu¬ 
nicating with the lungs by small air-cells; which facts may 
be shewn by various experiments on living and dead birds. 
These receptacles of air, of course, serve the purpose of 
lightening the body of the bird in order to facilitate its mo¬ 
tions. This effect is produced in most birds to assist their 
flight; in some aquatic species, for the purpose of swim¬ 
ming ; in the ostrich and some others for running. Hence 
we find the largest and most numerous bony cells in birds 
which have the highest and most rapid flight, as the eagle, 
&c. And hence also the bones of the bird which has just lelt 
the egg, are filled with a bloody marrow, which is absorbed 
soon alter birth, entirely in some, in others, particularly 
among the aquatic species, for the greater part. In many 
birds the interval between the two tables of the cranium 
contains air, but the apertures for its admission are not 
connected with the lungs, but merely with the Eustachian 
tube. The same, also, is the case with the immense bill of 
some birds, which are for that reason called levirostres. 
The lungs of quadrupeds agree on the whole in structure, 
form, and connexion, with those of the human subject. In 
the cetacea, on the contrary, and in the web-footed mam¬ 
malia (as the manati), which approach most nearly to them, 
they are distinguished by a firmer texture, particularly of the 
investing membrane, and by their peculiar form ; since they 
are not divided into lobes, but have an elongated and flat¬ 
tened appearance. They are adherent to the pleura, as well 
as to the very strong and muscular diaphragm. 
The annexed figures shew the parts of the circulating and 
respiratory systems in the different classes. 
In fig. 17 we see the heart of the barnacle, where a a shews 
the heart situated in the intestine near the stomach; b, four 
large vessels which arise from its upper extremity ; and t, 
two smaller ones, the larger of which is thin skinned, the 
smaller of thick parietes; it terminates at d, in several ramifi¬ 
cations. The exterior of this creature’s heart is irregularly 
furrowed. Within it is, as in more perfect animals, fur¬ 
nished with fleshy fibres. It has no auricle. The same 
vessels ramify on the gills as furnish the rest of the body. 
Fig. 27, the heart of the saepia officinalis: a, the heart 
situate in the abdomen; it is a full muscle, oblong and tri¬ 
angular, smooth externally ; the interior, moderately iurnished 
with fibres, hath many anfractuodties; b b, the auricles, two 
in number, cut off at the origin of the pulmonary vessels. 
At fig. 21 is seen the heart of the bee. It is situaled along 
the back as in silkworms, &c. It is a long tube bulging a 
little in places, fibrous and strong, and is marked a a ; on 
each of its sides the delicate tracheae, b b, are situated. These 
are spread out upon very fine membranes, c c, which serve 
also to contain fat; amid this fat muscular fibres may be 
seen, which have been conjectured to be useful in the cir¬ 
culation, by contracting and pressing the sides of the heart, 
and to press also the air from the tracheae into it; f ff mark 
the situation of muscular fibres that serve for the movement 
of the abdominal rings. The figures 1, 2, 3, 4, 5, indicate 
these abdominal rings. 
The ovary is seen in the same figure, marked e e. There 
are two ovaries in most insects, and in some more removed 
from one another than in others. 
At fig. 22 we have a representation of the heart in the com¬ 
mon garden caterpillar, marked a. This organ is a small thin 
oblong canal, furnished with transverse contractile rings and 
longitudinal bands, that passes along the body, traversing suc¬ 
cessively the tail, abdomen, thorax, and penetraling some way 
into the brain. This canal has enlargements in different parts, 
and a multitude of tracheae ramify on its surface. The mus¬ 
cular fibres previously described, produce contractions of 
