ORDERS OF FISHES. ; 241 
4. Besides the “‘ paired” fins which represent the limbs, there 
is also a series of uzpaired or “median” fins, the rays of which 
are supported upon a series of dagger-shaped bones, deeply 
plunged in the flesh in the middle line of the body, and known 
as the “interspinous” bones (fig. 123). The median fins are 
variable in number, but when fully developed they consist of 
one or two fins on the back (the dorsal fins), one or two on the 
ventral surface (the anal fins), and one clothing the posterior 
extremity of the body (the caudal fin, or tail, fig. 124). Inallthe 
Teleostei, the caudal fin has the shape called “ homocercal”—that 
is to say, it consists of two equal lobes—and the vertebral column 
is not prolonged into the upper lobe (fig. 125, a). 
5. The heart consists of two cavities, an auricle and a ven- 
tricle, but the da/bus arteriosus is not rhythmically contractile, 
and is separated from the ventricle by only a single pair of 
valves. 
6, The respiratory organs are in the form of free, comb-like, 
or tufted gills, enclosed in two cavities placed on the sides of the 
neck. Each of these branchial chambers opens externally by 
a single aperture, the “ gill-slit,’ which is protected by a chain 
of bones, forming the “ gill-cover,’? and by a membrane sup- 
ported by bony rays. Internally the branchial chambers com- 
municate with the throat by a series of clefts or fissures, and 
the water required in respiration is taken in at the mouth bya 
process analogous to swallowing. 
7. The nasal sacs never communicate behind with the throat 
(pharynx), 
TABULAR VIEW OF THE MAIN DIVISIONS OF THE TELEOSTEI. 
SUB-ORDER I, MALACOPTERI.—USually a complete series of fins, sup- 
ported by rays, all of which are so//, or many-jointed (with the occasional 
exception of the first rays in the dorsal and pectoral fins). A swim- 
bladder is always present, and is always connected with the gullet by'a 
duct. The skin is rarely naked, and is mostly furnished with cycloid 
scales, but sometimes ganoid scales are present. 
Amongst the more important families in this sub-order are the Eels 
(Murenide), Herrings (Clupeide), Pikes (Esocide), Carps (Cyprinidae), 
Salmon and Trout (Sadmonide), and Sheat-fishes (Szluride). 
SUB-ORDER IT. ANACANTHINI.—Fins entirely supported by soft rays, 
and never by spinous rays, Ventral fins either wanting, or placed 
under the throat, beneath or in advance of the pectorals. 
The two leading families in this sub-order are the Cod, Ling, and 
Q 
