AND ON THE CLASSIFICATION OF FISH. 525 
which occurs among the Ganoids. The rounded caudal fin and 
the anal fin consist of articulated rays. Those of the caudal 
fin are placed both above and below the spine. The anterior 
margins of the fins are not covered with spinous plates. Of the 
fins, the pectoral and ventral fins are remarkable, the former 
for a scaly somewhat elongated limb; and its posterior surface, 
which differs from all the other fins, is covered with very small 
scales between the fin-rays; the ventral fins, by the peculiar 
character of containing the bones of a middle foot in addition to 
the fin-rays. The lingual bone is composed of three parts; its 
body, which receives the gill-arches, is very large and simple. 
Beneath the lingual bone, where in other fishes the hyoidal 
keel projects against the clavicle and is immediately combined 
with it, in Polypterus there are two bones, one on each side; 
they are fixed between the middle and the most inferior por- 
tion of the horn of the tongue-bone. These bones are attached 
by ligaments to a third isolated piece, which connects them 
with the clavicle. The nose has a more complex structure than 
that of any other fish. In the large cavity, which is covered by 
the true nasal bones, is situated a labyrinth of five nasal pass- 
ages; these are parallel to an axis, and thus form a prismatic 
elongated star. Each of these canals contains in its interior the 
gill-like arrangement of folds, which only occurs in one other 
instance amongst fishes. The anterior nasal aperture is pro- 
longed into a membranous tube, the posterior is a small cleft in 
the cutaneous tegument anterior to the eye. The stomach forms 
a blind pouch, the pylorus a blind intestine; below the pylorus 
the intestine contains the spiral valves. The swimming-bladder 
is double, and consists of two unequally long sacs, that ante- 
riorly coalesce into a short common cavity, which opens in a 
different manner from that of all other fishes, as I have elsewhere 
shown, not into the upper wall of the throat, but, like a lung, 
into the ventral wall, by a long fissure. However, these organs 
are not lungs, for they receive bright red blood, like all other 
parts of the body, from their artery, which is a branch of the 
last gill-vein, which itself proceeds towards the sac of the swim- 
ming-bladder. The veins of the swimming-bladder unite with 
the veins of the trunk, viz. with the hepatic veins. These sacs 
are not cellular, and are covered in their entire circumference by 
a muscular tunic. 
The second section of the Ganoids contains the Sturgeons 
with only partial osseous spinal columns. Artedi, Gronovius 
