GENERAL CHARACTERS OF FISHES. 411 
Laboratory Work.—The anatomy of these animals is exceedingly in- 
teresting ; the respiratory sacs and nasal duct can be exposed by a lon- 
gitudinal section of the head ; the relations of the notochord can be 
best seen by transverse sections ; the heart and vessels should be in- 
jected. Preparations of the brain should be made, and with care the 
skull prepared. See Miller, 1835-45, W. B. Scott (Journ. Morphology, 
1888), 
Crass IV. Pisces (Sharks, Rays, Sturgeons, Garpikes, and 
bony fishes). 
General Characters of Fishes*—We now come to Verte- 
brates which have genuine jaw-bones and paired fins, and 
which, in short, are affiliated to the Batrachians, and through 
them with the reptiles, birds, and mammals. All the fishes 
agree in having a true skull, to which is attached a movable 
lower jaw. The brain is well developed, with its lobes for 
the most part, at least, equivalent to or homologous with 
those of the reptiles, birds, and mammals, though the cere- 
bral hemispheres are small, and in most fishes of nearly the 
same size as the optic lobes; the cerebellum is also generally: 
Dorsal fin. 
Cauda. = 
Anal. Ventral. Pectoral, 
Fig, 888.— The Mud-Minnow. 
of moderate size. The head forms part of the trunk, there 
being no neck (except in the Hippocampide), and the body 
is usually compressed and adapted in shape for rapid motion 
in the water. 
Paired fins are always primitively developed, though the 
posterior or ventral fins, at least, are in many cases wanting 
through the atrophy of parts developed in embryonic life. 
The pectoral and ventral fins (Fig. 388), which represent the 
fore and hind legs of higher Vertebrates, are attached to the 
body or trunk by a shoulder and pelvic girdle. The shouldet 
* Giinther’s Introduction to the Study of Fishes. London, 1880. 
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