The Rattlesnake (_Crotalus horridus_) is one of the deadliest of venomous serpents, is frequently six feet in length, and as thick as a man's leg. But Providence has furnished it with an antidote against its own poison, or, at least, with an instrument which makes it its own betrayer, and warns man involuntarily against its formidable presence. This is the _rattle_ to which it owes its vulgar appellation. The rattle is situated at the end of the tail, and consists of several hard, dry, bony processes. Imagine a string of hollow, dry, semi-transparent bones, nearly of the same size and figure, and resembling to some extent the shape of the human _os sacrum_: imagine these so placed that the tip of every uppermost bone runs within two of the bones below it; imagine these constantly clattering against each other, as the reptile moves, with a hoarse, dull, echoing sound, and you will be able to form some idea of the permanent warning of its approach which the Crotalus carries about with it. The rattle is placed with the broad part perpendicular to the body, and not horizontal; and the first joint is attached to the last vertebra of the tail by means of a thick muscle beneath it, no less than by the membranes which unite it to the skin. The bony rings increase in number with the reptile's age, and it gains an additional one, it is said, at each casting of the skin. [Illustration: CROTALUS, AND BOA-CONSTRICTOR.] The _Crotalus horridus_ is of a yellowish-brown colour, varied with patches of a deeper hue, and from the head to some distance down the neck run two or three longitudinal stripes of the same. Its habits are sluggish; it moves slowly, and only bites when angered, or for the purpose of killing its prey. It is provided with two kinds of teeth--viz., the smaller, which, planted in each jaw, serve to catch and retain the food; and secondly, the fangs or poisonous teeth, which kill the prey, and are placed outside the upper jaw. It feeds principally upon the smaller mammals and upon birds, which it seems certain it possesses a peculiar power of fascinating--the effect, it may be, of intense fear. "When the piercing eye of the rattlesnake is fixed on them," says Mr. Murray, "terror and amazement render them incapable of escaping; and, while involuntarily keeping their eyes fixed on those of the reptile, birds have been seen to drop into its mouth, as if paralyzed, squirrels descend from their trees, and leverets run into the jaws of the expecting devourer." Hogs and peccaries, however, are unaffected by this panic, and feed greedily upon the reptile which causes it, whose venomous fangs cannot penetrate their formidable hide. Its poison, once imbibed, is very fatal, acting upon man and the larger mammals, such as the horse or ass, in a few hours. [Illustration: TRIGONOCEPHALUS PURSUED BY BIRDS.]