SIREN.
The nantes, or swimming amphibia, characterized by their having fins, and by breathing by means of lateral gills, were afterwards distributed into the or ders of fishes denominated branchiostigi, and chondropterygii; which have since been ranked by Dr. Shaw, and others, under the general term cartilaginous fishes. See CRRONDROPTERIGIOVS.
We have thought it right to give this account of the changes in the Linnzan system, which we have generally adopt ed, having omitted any mention of the facts under the former articles. " Ser pents," says the translator of Gmelin, " are cast naked upon the earth, without limbs, exposed to every injury, but fre quently armed with a poison the most deadly and horrible : this is contained in tubular fangs resembling teeth, placed without the upper jaw, protruded or re tracted at pleasure, and surrounded with a glandular vesicle, by which this fatal fluid is secreted : but lest this tribe should ton much encroach upon the limits of other animals, the benevolent Author of nature has armed about a fifth part only in this dreadful manner, and has ordained that , all should cast their skins, in order to inspire a neces sary suspicion of the whole. The jaws are dilatable, and not articulate, and the cesophagns so lax, that they can swal low without any mastication, an ani. mal twice as thrice as large as the neck : the colour is variable, and changes, according to the season, age, or mode of living, and frequently va nishes, or turns to another in the dead body : tongue filiform, bifid ; skin reti culate." The distinction between the poisonous and innoxious serpents is on ly to be known by an accurate exami nation of their teeth ; those which are poisonous being always tubular, and cal culated for the injection of the poisonous fluid, from a peculiar reservoir commu nicating with the fang on each side of the head. These teeth or fangs are
situated in the upper jaw : they are frequently accompanied by smaller fangs, seemingly intended to supply the place of the others, if lost by age or accident. The fangs are situated in a peculiar bone, so articulated with the rest of the jaw as to elevate or depress them at the pleasure of the animal : in a qui escent state, they are recumbent, with their points directed inwards or back wards ; but when the animal is inclin ed to use them as weapons of offence, their position is altered by the peculiar mechanism of the bone in which they are rooted, and they become almost per pendicular.
Serpents in cold and temperate cli mates dunces! themselves, during win ter, in cavities, beneath the surface of the ground, or in any other convenient places of retirement, where they become near ly or wholly in a state of torpidity. Some serpents are viviparous, as the rattle snake, the viper, &c. : while the innoxi ous species are oviparous, depositing, as we have observed, their eggs in a kind of chain in any warm and close situation, where they are afterwards hatched. The broad undivided lamina on the bellies of serpents are termed scuts, and the smaller or divided ones beneath the tad are called subcaudal scales, and from these different kinds of lamina: the Linnzan genera are charac terized,