SPINY-FINNED FISHES, 
53 
ORDER I. ACANTHOPTERYGII. 
j {spiny-finned Fishes.) 
The skeleton in this large and very natural 
Order is composed of bone ; the first rays (count- 
; ing from the head backward), of the dorsal fin, 
of the pectorals, and of the anal, and, generally 
the first ray of the ventrals are unjointed, in- 
flexible, and spinous. When there is more than 
one dorsal, the anterior is entirely filled with 
> spinous rays. In some cases, as in the common 
! Sticklebacks, the spinous rays are unconnected 
by a common membrane, and form free spines. 
The- ventrals are, for the most part beneath the 
pectorals, or even in advance of them. The body 
is clothed with scales formed of successive laminae 
or layers of horn-like, unenamelled bone, which 
i have their free hinder margin cut into teeth. 
The swimming-bladder is not furnished with an 
air-duct leading into the gullet. 
Nearly two-thirds of the species belonging to 
the whole Class of Fishes are found in this Order, 
which are scattered over all parts of the world, 
both in fresh and salt waters. Many of them are 
I distinguished for elegance of form and beauty of 
I colour ; nearly all are fit for food, and some, as 
the Mackerel family, including the Tunny, sup- 
port important fisheries. 
The form of the dorsal fin is subject to much 
variation in this Order. Nearly half of the 
species have it divided into two, a spinous and a 
