In all the Amphibia
, a glottis, placed on
the ventral wall of the oesophagus, opens into a
short laryngo-tracheal chamber with which two
pulmonary sacs are connected, either directly,
or by the intermediation of bronchi (as in the Aglossa
), or by a trachea (as in the Gymnophiona
The walls of the pulmonary sacs
are more or less sacculated. In most Amphibia
the lungs are equal in size; but in the
, the right is much
smaller than the left. In Proteus
, the pulmonary
blood is not all returned to the heart,
some of it entering the veins of the trunk.
Aerial respiration is effected, in the Amphibia
by pumping the air from the oral cavity into
the lungs. To this end the mouth is kept
Shut, and ingress and egress to the air is given
by the nasal passages, which always open
immidiately behind the vomers, at the anterior
part of the roof of the mouth. These passages
being open, and the hyoidean apparatus depressed,
the air fills the cavity of the mouth. The external nortils
are than shut, and, the hyoidean apparatus being raised, the air is forced, through the open glottis,
into the lungs.
|Fig. 59. - The brain of Rana esculenta from above, magnified four times; L.ol.,the rhinencephalon, or olfactory jobes, with, I., the olfactory nerves; Hc., the cerebral hemispheres; Fh. o., the thalamencephalon with the pineal glaud, Pn., L. op., optic lobes; C., cerebellum; S. rh., the fourth ventricle; Mo., medulla oblongata.
posscss a urinary bladder,
which opens into the cloaca, and does not receive the ureters.
The kidneys of the Amphibia
appear, like those of fishes, to
be persistent Wolffian bodies.
In the brain of the Amphibia
the cerebellum is always
very small, and represented by a mere band; the cerebral hemispheres are elongated, and contain ventricles. In Proteus
the mesencephalon is very indistinctly marked. The optic
nerves form a chiasma.
As in fishes, the pneumogastric gives off a lateral nerve,
which runs along the sides of the body.
The eyes are very small, and covered by the integument,
, the Gymnophiona
, and the genus Pipa
perennibranchiate and derotreme Urodela
have no eyelids;
but most Batrachia
have not only a well-developed upper
eyelid, but a nictitating membrane, moved by special muscles.
possess a fenestra ovalis with a cartilaginous,
or osseous, columelliform stapes, the expanded proximal
end of which is fixed to the membrane of the fenestra. In
, if not in all, there is a fenestra rotunda,
though the presence of a distinct cochlea has not been ascertained.
, the Gymnophiona
, and the Pelobatidea
among the Batrachia
, have no tympanic cavity, nor membrane.
In the other Batrachia
there are tympanic cavities
communicating freely with the throat. Each is closed externally
by a tympanic membrane, with which the outer extremity
of the stem of the stapes is connected. In the Aglossa
two tympanic cavities communicate with the mouth by a single
Eustachian aperture; and the outer end of the stapes expands
into a great cartilaginous plate coextensive with the tympanic
The ducts of the reproductive organs of the Amphibia
like those of the Ganoidei
, always communicate directly with
the urinary ducts: and, as in most Ganoidei
and all Elasmohranchii
the proximal end of the oviduct is open, and communicates
with the peritoneal cavity. The male has no penis,
unless a papillary elevation of the wall of the cloaca may represent
such an organ. The testes of the male Amphibia
composed of tubules, and vasa efferentia
convey the contents
of these away. In the Urodela
, the vasa efferentia
testis enter the inner side of the corresponding kidney, and
traverse it, leaving its outer side to enter a genito-urinary duct
, which lies on the outer side of the kidney, ends blindly
in front, and opens behind into the cloaca. The uriniferous
tubuli also pass directly from the outer margin of the kidneys
into the genito-urinary duct. In the Batrachia
there is likewise
a genito-urinary duct, and the vasa efferentia
run to the
inner edge of the kidney and enter it. In Bombinator igneua
and Discoglossus pictus
, the genito-urinary duct receives the
urinary products and the spermatozoa, in the same way as in
. But, in the Frogs and Toads, the urinary tubuli
are gathered together into a special small canal which opens
into the genito-urinary duct near its termination in the cloaca,
and the vasa efferentia
pour their contents into this canal. Under these circumstances, the part of the genito-urinary duct
which lies beyond the renal canal may become obliterated, as
in the Frogs; or may persist, and play the part of a vesicula
, as in the Toads.
In the female Amphibia
, the kidneys have, as in the male
Frogs and Toads, a renal canal which opens into the lower
part of the oviduct.
It would appear from these facts that the oviduct in the
female, and the genito-urinary ducts in the male, Amphibia
represent both the Wolffian and the Mullerian ducts of the
In most Amphibia
the ova are impregnated and hatched
outside the body, but internal impregnation and incubation
occur in some of the Urodela
. In Pipa
the eggs are hatched
in pouches of the dorsal integument, while the male Alytes
carries them twisted in strings round his legs.
When hatched, the young are devoid of respiratory organs
and of limbs, and are provided with a long tail, by means
of which they swim about. Branchial clefts soon make their
appearance; and ciliated external branchial plumes, like those
of the perennibranchiate Urodela
, are developed. A pair of
suckers are sometimes formed upon the under-surface of the
mandibular region, and the jaws acquire horny sheaths.
A broad opercular membrane is developed in front of the
branchial aperture, and, in the Batrachia, extends over and
eventually covers the gills, a rounded aperture persisting for
a certain time only on the left side. The anterior pair of limbs
is developed before the posterior, but in the Frog they are not
so soon visible, being hidden by the opercular membrane.
The lungs make their appearance as diverticula of the
ventral wall of the oesophagus. The nasal sacs are at first
mere caecal involutions of the integument, but nasal passages
communicating with the mouth are soon formed, and both
aerial and aquatic respiration are completely established.
In the Batrachia
, as development proceeds, the external
branchiae disappear, and are succeeded, functionally, by short
branchial filaments developed upon the whole length of each
of the branchial arches, of which there are four.
|Fig. 60. - A. B. Tadpoles with external branchlae: n, nasal sacs: a, eye; o, ear; k b, branchiae; m, mouth; z, horny jaws; s, suckers; d, opercular fold.
C., a more advanced Frog's larva: y, the rudiment of tne hind-limb; k, s, the single branchial
aperture. The figure has not been reversed, so that this aperture appears to lie on the
nght side instead of the left.
Before the development of the lungs the heart has only
a single auricle; afterward, the auricle becomes divided into
two. The aortic arches, at first, pass along the visceral and
branchial arches to the dorsal aorta, as in other vertebrate
embryos. When external gills are developed, each receives a
loop from the corresponding arch, much as in Proteus
When the internal gills of the Batrachia
aortic arch which belongs to a branchial arch splits into two
trunks, - one which remains directly connected with the cardiac
aorta, and another which opens into the dorsal aorta. The
vessels of the branchial filaments constitute loops between
these afferent and efferent trunks, which always remain united
by anastomoses. When branchial respiration ceases, and the
branchial processes and their vessels disappear, the anastomoses
dilate; the direct communication between the afferent
and efferent trunks of the second pair of internal branchiae ia
reestablished; and they become the permanent arches of the
aorta. The anterior branchiae are replaced by the carotid
glands, and their afferent vessel is the carotid passage of the
adult. The afferent and efferent trunks of the third pair of
branchiae are converted into the stem of the cutaneous artery,
and the afferent trunk of the fourth pair of branchiae into that
of the pulmonary artery. The diagram (Fig. 25, p. 83) is
intended to make these changes, and the relations of the
various trunks to the embryonic aortic arches, intelligible.
The alimentary canal of the Tadpole is, at first, long, and
coiled up into a close spire, like a watch-spring, in the abdomen,
but its length becomes relatively less as age advances.
At the same time, the diet changes from vegetable to animal-the young tadpole being chiefly herbivorous, the adult,