ANATOMY AND PHYSIOLOGY OF SERPENTS.
The skin of serpents consists chiefly of a cuticle and corium. The cuticle exhibits considerable differences in thickness, and, as happens to the lizards, is periodi cally cast off and PCDOVed. The corium is destitute of a villous surface, and intimately connected with the muscular web underneath. The appendices of the skin consist exclusively of scales. These are divided by na turalists into two kinds. The true scales, or squamer, are usually produced longitudinally, and pointed or rounded posteriorly. They have, in general, some as perities on the surface. The shields or max are of much larger dimensions, and pioduccd qansversely. In some cases they embrace the whole of the body, forming rings ; in other cascs a half or a quarter of one side only. They usually present a smooth surface, and occur chiefly on the belly, between the throat and vent. They differ considerably in number in different species, and even in individuals of the same genus, so that the character fur nished by their number, should be employed with cau tion in the discrimination of species. There does not appear to be any well marked secretion from the skin, nor are there many species which have glands from which it could proceed. Between the nose and the eye, indeed, on each side, there is a bag or erumen in some species, not unlike the bags which occupy the same po sition in some of the ruminating animals. Here, how ever, there is no appearance of glandular sti ucture yet discovered, and the cuticle with which they ate lined appears continuous, and lalls off along with that which covers the rest of the body. Dr. Tyson first observed these crumens in thc rattlesnake; anti Dr. Russel and Sir E. Home have since attended to their structure more pal ticulatly. The last of these observers, when consi dering their use, offers the followiny; remarks : As amphibious animals, in general, have no glands to supply the skin with moisture froni within, but receive it by coming in contact with moist substances, it is possible the bags in the snaKe may be supplied in that manner, and the more so, as the cuticular lining appears perfect.
Another peculiarity is remarkable in snakes fur nished with the bags describer' above, namely, an oval cavity, situated between the bag and the eye, the open ing into which is within the inner angle of the eye-lid, and directed towards the cornea. In this opening there are two rows of projections, which appear to form an orifice capable of dilatation and contraction. From the situation of these oval cavities they must be considered as reservoirs for a fluid, which is occasionally to be spread over the cornea ; and they may be filled by the falling of the dew, or the moisture shaken from the grass through which the snake passes." Phil. Trans. 1804, p. 74.
The osseous systerr4 of serpents is chiefly character ized by the articulation of the vertebrx, the number of ribs, and the absence of the extremities. The head is connected with the atlas by a single tubercle, having three articular surfaces. The posterior articular sur face of each vertebra is in the form of a rounded emi nence, which is received into a corresponding depres sion in the anterior end of the one which follows. There is thus throughout the vertebral column a series of ball and socket joints, admitting a great extent cf flexure, in some cases restrained by the spinous or articular pro cesses. The ribs in some species amount to nearly three hundred pairs. The dorsal extremitie.s of the ribs are enlarged with a terminal depression, which receives a rounded protuberance of the vertebrae. Each vertebra, therefore, has a rib on each side, united by a modified ball and socket joint. These ribs are not continued be yond the anus. They embrace a great part of the sides, and terminate in cartilaginous processes united to the scales of the belly. AI. Lacepede has remarked hi the viper, boa, and rattlesnake, that there are uniformly two ribs and one vertebra corresponding to each shield of the belly. In one small group some of the ribs are united by cartilaginous productions on the belly ; and there is even the rudiment of a sternum.