Structure of the poison teeth of the Rattlesnake.

Fig. 337. Structure of the poison-teeth of the Rattlesnake.

* In the collection of Professor Bell there is a small snake which, having by mishap attempted to swallow a mouse of too large size, and being quite unable, in consequence of the mechanism referred to, to disgorge it, was found dead, and the skin and muscles of its neck absolutely rent from excessive stretching.

1 Memoire sur les caracteres tires de 1'Anatomie pour distinguer les Serpens venimeux des Serpens non-venimeux; par M. Duvernoy (Ann. des Sc. Nat. xxvi.).

(1921). Behind the large poison-fang in use, the capsule that encloses it generally contains the germs of several others, ready to supply its place should the former be broken off; and in the event of such an accident, one of these supplementary teeth soon becomes consolidated with the superior maxilla, and adapted in all respects to take upon itself the terrible office of its predecessor.

(1922). Dreadful as are the means of offence thus conferred upon the poisonous serpents, it is impossible to avoid noticing in this place that admirable provision of Nature which, in one genus at least, serves to give timely warning of the vicinity of such dangerous assailants. We need merely mention the rattle of the Rattlesnakes (Crotalus) - an organ the intention of which is so obvious that the most obtuse cannot contemplate it without at once appreciating the beauty of the contrivance. This singular rattle is formed of numerous horny rings, that are in fact merely modifications of the general scaly covering of the reptile, so loosely articulated together that the slightest movement of their formidable possessor is betrayed by the startling noise produced by the collision of the different pieces composing the organ: even when at rest, the creature announces by rapid vibrations of the tail the place of its concealment, apparently to caution the inadvertent intruder against too near an approach.

(1923). In the grand police of Nature, the scavengers are by no means the least important agents. In hot climates especially, where putrefaction advances with so much rapidity, were there not efficient and active officers continually employed in speedily removing all dead carcases and carrion, the air would be perpetually contaminated with pestilential effluvia, and entire regions rendered unhabitable by the accumulation of putrefying flesh. Perhaps, however, no localities could be pointed out more obnoxious to such a frightful cause of pestilence than the banks of the tropical rivers - those gigantic streams which, pouring their waters from realm to realm, daily roll down towards the sea the bloated remains of thousands of creatures which taint the atmosphere by their decomposition.

(1924). Such are precisely the situations inhabited by Crocodiles and Alligators, the largest of the Saurian reptiles now in existence, animals in every way designed by Nature to feed upon putrefying materials: their tongue (fig. 338, d) scarcely projects from the lining membrane of the mouth, and its surface (e) is studded with large glands; the whole interior of the mouth is in fact, from its construction, little adapted to gustation.

(1925). The Crocodile, nevertheless, likewise kills living prey, which, from the structure of its teeth, it is obliged to effect by dragging its victim into the water and there drowning it. This mode of proceeding, however, simple as it might appear, involves many difficulties. As the reptile has no other instruments of prehension besides its mouth, and is obliged to hold its struggling prey submersed by the strength of its formidable jaws, it is manifest that, without some special contrivance, the water rushing into the throat of the Crocodile would prevent it from breathing quite as effectually as the animal it endeavours to drown; it might therefore become a question which of the two would survive immersion longest. The mechanism employed under these circumstances to give the Crocodile the advantage over its prey is very complete: a broad cartilaginous plate (fig. 338,f) stands vertically from the os hyoides, and projects upwards into the back part of the mouth; a similar valve (g) hangs down from the back of the palate, so that the two together form a kind of flood-gate, which, when the mouth is widely opened, effects a complete partition between the cavity of the mouth and the fauces, where the aperture of the larynx (h) is situated. The nostrils, moreover, are placed quite at the extremity of the snout, and the nasal passages leading from them are prolonged through the whole length of the upper jaw until they communicate with the fauces, behind the velum of the palate (g.) Such being the arrangement, it is immediately obvious that, when the communication between the mouth and the fauces is cut off by means of the two valves (g,f), the Crocodile, by merely keeping the tip of its snout above the water, breathes with the utmost facility, and it is thus enabled to keep its prey submerged for any length of time that may be requisite to extinguish life.

Mouth of the Crocodile.

Fig. 338. Mouth of the Crocodile.

(1926). The teeth of the Crocodile and of the higher Saurians are not merely consolidated with the bones of the skull to which they are appended, but are implanted in sockets formed in the bones composing the upper and lower jaws. Each tooth is a simple hollow cone, and encloses a vascular pulp, from the surface of which the bony matter of the tooth was formed. When a tooth becomes old and worn, a second is secreted by the same pulp within the cavity of the first, and the original one is shed, so that a succession of teeth thus make their appearance.

(1927). The alimentary canal of Reptiles offers little that requires special description. The oesophagus (fig. 343, ff) is generally extremely capacious, and the stomach of very variable shape and capacity. The latter viscus is for the most part pyriform, tapering gradually towards the pylorus; such is the case in the Chelonia and in the Batrachoid Amphibia: in Serpents it resembles a long bowel, and is capable of extraordinary dilatation; and in the Perennibranchiate Amphibia, as in the Proteus (fig. 340, i) and the Menojpoma (fig. 343, g), it looks like a mere dilatation of the intestine.