|Fig. 51. - Tho Mudfish (Lepidosiren).
���� The "Mudfishes" of the rivers of the
east and west coasts of Africa and of eastern South America
are nearly transitional forms between the Pisces
and the Amphibia.
The eel-like body, covered with overlapping cycloid scales,
tapers to a point at its caudal extremity, and is provided with
two pairs of long, ribbon-like, pointed extremities, and with a
The spinal column consists of a thick notochord, invested
by a cartilaginous sheath, without any osscous or cartilaginous
vertebral centra. The proximal ends of ossified neural
arches, of ribs, and, in the caudal region, of inferior arches, are
imbedded in the sheath of the notochord.
Fin-rays support the median fin. The skull, the palato-quadrate,
and suspensorial apparatus, form, as in Chimaera
one continuous cartilaginous mass, into the base of which the
notochord penetrates, terminating in a point behind the pituitary
No cartilage bone is developed in the place of the basi-occipital,
supra-occipital basisphenoid, or presphenoid; and there
are only two such ossifications, which represent the ex-occipitals
) in the side-walls of the cranium. A large parasphenoid
) underlies the base of the skull. Upon its roof a great single
), answering to the parietals and frontals, extends
from the occipital to the ethmoidal regions. In front of this
are two nasal bones (C
). There is no alisphenoid, but the
fronto-parietal and parasphenoid send processes toward one
another, which unite in front of the exit of the third division
of the fifth nerve. There is no interorbital septum, and the
cavity of the skull remains of tolerably even diameter throughout.
In front of the exit of the optic nerves, however, it is
longitudinally divided by a membranous septum.
|Fig. 52. - Skull ot Lepidosiren annectens: A, the oarieto-frontal bone; B, the supra-orbital; C, the nasal; D, the palato-pteryg:oid; E, tne vomerine teeth; E, O., the ex-occiptal; Mn, the mandible; Hy, the hyoid; Br, the branchiostegal rays; Op, the opercular
plate: x, the parasphenoid; y, the pharyngo-branchial; Or, the orbit; Au, the auditory
chamber; N, the nasal sac.
The ethmovomerine cartilage is continued to the anterior
extremity of the skull. It bears teeth, but no distinct vomer.
A great palato-pterygoid osseous arch (D
) extends from
the middle line along the upper and the under surface of the
palato-quadrate arch on each side to near the articular surface
of the mandible. In the middle of the roof of the mouth, divergent,
cutting, dentary plates are developed upon it. An
osseous nodule lies in the articular head of the palato-quadrate
cartilage, and is continuous with the bone F.
The mandible presents dentary plates corresponding with
those of the palate, and biting between the latter. The hyoidean
arch is attached to the posterior and lower edge of the
suspensorium - which bears a bony ray representing an operculum -
while the hyoidean arch itself carries a single branchiostegal
The pectoral arch is composed of a median cartilaginous
part, with two lateral portions of cartilage, at once separated
from, and connected with, the median cartilage by bone. The
bone is separated from the cartilage by a layer of connective
tissue, and seems to represent the clavicle, while the cartilage
answers to the coalescent coraco-scapular cartilages of other
The filiform fin is supported by a many-jointed cartilaginous
rod, articulated proximally with the coraco-scapular.
Upon this are disposed fine fin-rays like those of the Elasmobranchs,
which support the marginal fringe of the fin. The
ventral fin has the same structure as the pectoral.
|Fig. 58. - Longitudinal and vertical section of the skull of Lepidosiren, The cartilage is
dotted; the membranous and bony constituents are shaded with lines. A, B, C, D, E, Hy as in the preceding figure; a, a, the parasphenoid; P, S1, cartilaginous presphenoidal
region; ch, notochord; Au, situation of auditory chamber; 1, 2, first and second
vertebrae; II, V, VIII, exits of optic, trigeminal, and vagus nerves; a, quadrato-mandilbular
The intestine possesses a spiral valve, and the rectum
opens into a cloaca. The lungs have remarkably stiff walls,
and extend through the greater part of the body, beneath the
spine. The glottis, opening upon the ventral wall of the
gullet, places them in communication with the cavity of the
mouth, into which the nasal sacs open by posterior apertures,
which lie inside the upper lip and constitute true posterior
nares. The heart has a small, but distinct, left auricle, into
which the blood which has been aerated in the lungs is returned.
In addition to lungs, Lepidosiren
possesses both internal
and external gills, but the latter are rudimentary in the
The different species seem to differ in the manner in which
the primitive aortic arches are metamorphosed; but it may be
said, generally, that the first has disappeared; the second supplies
an internal branchia developed upon the hyoidean arch;
the third gives off the anterior carotid artery, and supplies
neither internal nor external branchia; the fourth supplies
only the first external branchia; the fifth and sixth supply
both internal and external branchiae; while the seventh is
connected only with an internal branchia. The pulmonary
artery seems originally to have been given off from an eighth
It is a remarkable circumstance that, while the Dipnoi
in so many respects, a transition between the piscine and
the amphibian types of structure, the spinal column and the
limbs should be not only piscine, but more nearly related to
those of the most ancient Crossopterygian
Ganoids than to
those of any other fishes.