1830-3 
of certain Fishes of the Ganges. 
175 
surface of the vertebrae, with the base of the cranium. All the arches are smooth on 
their internal surface. The hones corresponding to the scapulae, or those which 
in fishes support the pectoral fins, are long, slightly curved, and united by cartilage 
at their inferior extremities. 
Connected with deglutition and situate below each of the latter, is a small bone, 
which, together with the pharyngeal bones, is covered on the side next to the gullet, 
with small teeth. The body of each vertebra is hollowed out posteriorly, forming a 
heuii-spherical cavity, in which the inner vertebral fluid is contained, and is united 
through the nediuin of this substance, and also by a small triangular process sent off 
from each side of the cavity of the medulla spinalis, with the bone contiguous to it. 
The spinous process is bifurcated, or rather consists of two distinct pieces inclining in 
different directions; and each transverse one, of a short thick spine, grooved on its 
anterior aspect, with a thin plate of a triangular figure arising from it behind, and 
occupying the whole side of the body of the bone. The ribs, which are extremely 
small, are attached to the points of these processes as far as the anus. The cer- 
vical and caudal vertebrae are distinguished from the intermediate or dorsal ones : 
the former by the compressed flattened appearance of their bodies, the latter by 
possessing spinous processes both above and below. 
Organs of sense. That of smelling appears to be the most perfect. The 
nasal cavity of each side is tubular, and has two apertures, an anterior one at the 
extremity of the snout, and a posterior between the eyes : and consists also of two 
parts, one running forwards, the other extending backwards from the anterior open - 
ing in a duplicature of the membrane connecting the malar and maxillary bones, 
as far as the point of union between the latter and the coronoid process of the low- 
er jaw. The cavities of both the sides have a free communication with each other, 
at their anterior extremities, and may be filled with vermilion injection from one 
of the apertures. The eyes are very small, and are covered anteriorly by a trans- 
parent skin. The thalami optici lie behind the cerebrum, and send out two long 
slender optic nerves, which cross each other without any incorporation of sub- 
stance. 
Organs of Respiration and Circulation. Upon the under surface of the throat 
there is a semilunar aperture, divided below the integuments in the mesial line of 
the body into two smallar openings, each of which leads to the gills of the corres- 
ponding side. The branchial arches are connected by a strong tendinous mem- 
brane, in which are three small openings of an irregular figure for the passage of 
the water from the mouth, and are covered below, for about one-third of their 
length, by a thick muscle proceeding from the bone corresponding to the scapula 
to be inserted into the os hyoides. Of all the arches, the second alone possesses 
laminae for the purpose of breathing; and these consist merely of a few long 
fibrils attached to the middle of the arch, and occupying but a very small ex- 
tent of its surface ; the third supports in the place of laminae, a thick and semi- 
transparent tissue, which in large individuals of the species presents a fringed or 
denticulated appearance at its edge, while the first and fourth are bare, having only 
the membrane that fills up the space between the arches reflected over them. The 
principal organs of respiration are two small bladders, which the animal has the 
power of filling with air, immediately derived from the atmosphere. They are placed 
behind the head, one on each side of the neck, above the superior or vertebral extre- 
mities of the branchial arches, and are covered over by the common integuments, 
presenting externally, when distended with air, two protuberances of a round 
shape. On dividing the skin, and reflecting it back, each bladder is found to 
be partially covered, at its anterior part, by a small and extremely thin operculum, 
joined to the upper part of the articular bone oftlie head, and connected below with 
a membrana branchiostega, which i3 supported by six osseous rays. The posterior 
portion of the organ extending beyond the edge of the operculum, is confined in 
its situation, by a broad but thin muscular expansion, running across it iu an ob- 
lique direction, from the tendinous sheath of the spinal muscles above, to the gill 
membrane below. These bladders, which are smooth, and highly vascular upon 
their internal surface, do not possess a laminated structure, such as that of the 
respiratory bags in the lamprey ; but present, when separated from their surround- 
ing attachments, and inflated with air, thin semi-transparent membranous parietes 
resembling the posterior portion of the lungs of serpents. Each communicates 
with the cavity of the mouth, by a wide semilunar opening between the os hyoides 
and the first branchial arch ; its lower margin, which is thick and prominent, is 
composed of several muscular fibres that extend between the end of the first 
branchial arch and the side of the spine, constituting a species of constrictor 
muscle, by means of which the aperture can be contracted to so small a size, 
