65 
The cartilaginous fishes are entirely without any 
maxillary or intermaxillary bones, their teeth being in¬ 
serted on the palate and vomer. Their skeleton is 
essentially cartilaginous, in which the calcareous matter 
is deposited in the form of grains, and their skull is 
formed of a single piece, without any suture. 
The Sturgeons ( Accipenser) have the gill-flap open 
like the other fishes. Their body is protected by bony 
plates implanted in the skin, and arranged in longitudinal 
rows ; their mouth is small, destitute of teeth, and 
placed at the base of an elongated muzzle. They 
ascend large rivers to spawn, and furnish one of the 
most profitable fisheries. Their flesh is excellent; 
their roe, dried and salted, forms caviar, and their 
swimming bladder, merely washed and dried, is the 
common isinglass of commerce. 
The Spatulariae (. Polyodon ) have a free gill-flap, like 
the Sturgeons, but their beak is long and spatula-shaped, 
and their mouth large and armed with teeth. 
The Chimerae ( Cliimcera ) have great affinity to the 
Sharks both in external form and the position of their 
fins, but their gill cavity opens externally by a single hole 
on each side, and is covered by the rudiments of a gill- 
flap. Between their eyes they have a fleshy process end¬ 
ing in a group of small spines. They lay very large eggs, 
with a coriaceous shell, of an ovate lanceolate shape. 
All the other cartilaginous fishes have their gills adhe¬ 
rent to the outer side of the gill cavity, allowing the water 
to escape through a series of holes between each gill. 
In most of these, as the Sharks and Rays (Squa¬ 
nder), the gills are laminar. The fish are furnished 
with large pectoral and ventral fins; and the mouth, 
which is usually placed under the end of the muzzle, is 
armed with teeth. 
The Sharks ( Squalus ) are distinguished by their 
elongated form, and large, fleshy tail, and by the gill 
aperture being placed on the side of the neck. Many of 
them are viviparous; others produce eggs inclosed in a 
hard, horny shell. They have been divided into several 
f genera, 
ROOM XI. 
Nat. Hist. 
