CHAPTER XIX.
OSSEI, OR BONY FISHES.
Under this denomination is comprehended many of the fishes which are most familiar to us. They are characterized, as we have said elsewhere, as a group of animals having a solid skeleton. They are divided into six orders; founded, however, it is necessary to add, on characteristics of little organic importance, and the names bestowed upon them are of a most barbarous description. These names are, I. Plectognathi, namely, fishes in which the upper jaw is attached to the cranium, from πλεκτὸς, interlaced, and γνάθος, jaw.
Afterwards those in which the upper jaw is movable, and the gills arranged in circles, like rounded hoops. These are, II. the Lophobranchii, from λὀφυς, crested, or aigrette, and βρἀνχια, gill.
In the other orders the gills are arranged in a comb-like form. These are divided into two great groups. In the first, the rays of the fins are soft, except occasionally the first of dorsal or pectoral fins. These are, III. the Malacopterygians, from μαλακὸς, soft, and πτερύγιον, finned—the third group of osseous fishes. In a later group the fish have bony rays to the anterior dorsal fins, some osseous rays, and the anal fin and generally one of the ventral fins. These are, IV. the Acanthopterygians, from ἂκανθα, spiny, and πτερύγιομ, finned, which form the last group of bony fishes.
I. Plectognathi.
From their organization the fishes of this order establish the passage from cartilaginous to the osseous fishes. Their skeleton, which remains for some time more or less soft, becomes finally hard. The chief characteristic of the order is that the maxillary is firmly attached to the side of the inter-maxillary bone which forms the jaw, and the arch of the palate is united to the skull in such a manner as to be motionless. The operculum and rays of the gills are hidden under a thick skin, which leaves externally only a small branchial slit. These fishes have no true ventral fin, and have only vestiges of side fins.
This order comprehends two natural families characterized by the armature of their jaws. They are the Gymnodonta and the Sclerodermata.
