this, for that they grow to such a size that in the belly of one killed on the Vatican Hill in the reign of Claudius an entire infant was found. Suetoniue (in Octay.' 43) mentions the exhibition of a serpent 50 cubits in length in front of the comitium. But without multiplying instances from /Elian and others, we will now come to more modern accounts. Bontius (v. 23) says, " The Indian serpents are so multitudinous that According to Pliny the name Doe was given to these serpents because they were said to be at first nourished by the milk of cows, and Johnston and others observe that they derived the name not so much from their power of swallowing oxen as from a story current in old times of their following the herds and sucking their udders. Boa is also stated by some to be the Brazilian name for a serpent.
Before entering upon the subdiviaione of this family we will examine seine of the moat remarkable points in the structure and organisation of the Heider.
On looking at the accompanying representation of the skeleton of a Boa Constrictor, drawn from the beautiful preparation in the British Museum, we first observe the strong closeeet teeth, of which there is a double row on each aide of the upper jaw, all pointing backwards, and giving the serpent the firmest hold of its struggling victim, which is thus deprived of the power of withdrawing itself when once locked within the deadly jaws. Serpents do not masticate. The prey is swallowed whole, and to assist deglutition their under jaw consists of two bones' easily separable at the symphysie, or point of junction, while the bone similar to the os quadratum in birds, by the inter vention of which it is fitted to the cranium, further facilitates the act The upper jaw moreover is so constructed as to admit of considerable motion.
We next observe the spine, formed for the most extensive mobility, and the multitude of ribs constructed as organs of rapid progression, when joined to the belly-scales, or scuts, with which the whole inferior surface of the body may be said to be shod. " When the snake," writes Sir Everard Home, " begins to put itself in motion, the ribs of the opposite sides aro drawn apart from each other, and the small cartilages at the end of them are bent upon the upper surfaces of the abdominal ecuta on which the ends of the ribs rest, and as the ribs move in pairs the scutum under each pair is carried along with it This scutum by its posterior edge lays hold of the ground, and becomes a fixed point from whence to set out anew. This motion is beautifully seen when a snake is climbing over an angle to get upon a flat surface. When the animal is moving it alters its shape from a circular or oval form to something approaching to a triangle, of which the surface on the ground forms the base. The coluber and boa having large abdominal nuts, which may be considered as hoofs or shoes, are the beet fitted for this kind of progressive motion." (' Lec tures on Comparative Anatomy,' voL 1) Sir Everard, in the same lecture, speaking of the ribs as organs of locomotion, says :—" An observation of Sir Joseph Banks during the exhibition of a coluber of unusual size first led to this discovery. While it was moving briskly along the carpet he said he thought he saw the ribs come forward in succession like the feet of a caterpillar. This remark led me to examine the animal's motion with more accuracy, and on putting the hand under its belly while the snake was in the act of passing over the palm the ends of the ribs were distinctly felt pressing upon the surface in regular succession, so as to leave no doubt of the ribs forming so many pairs of levers by which the animal moves its body from place to place." The merit however
of this discovery is due to the sharp-sighted Tyson, who was the first to observe the loconiotive power of the ribs of the Boa.
Sir Everard Home informs us by what. additional mechanism this faculty is effected: The ribs, be observes, are not articulated in snakes between the vertebra., but each vertebra has a rib attached to it by two slightly concave surfaces that move upon a convex protuberance on the side of the vertebra, by which means the extent of motion is unusually great ; and the lower end of each vertebra having a globular form fitted to a concavity in the upper end of the vertebra below it, they move readily on one another in all directions. The muscles which bring the ribs forward, according to Sir Everard, consist of five sets—one from the transverse process of each vertebra to the rib immediately behind it, which rib is attached to the next vertebra. The next set goes from the rib a little way from the spine, just beyond where the former terminates ; it passes over two ribs, sending a slip to each, and is inserted into the third : there is a slip also connecting it with the next muscle in succession. Under this is the third set, which arises from the posterior side of each rib, passes over two ribs, sending a lateral slip to the next muscle, and is inserted into the third rib behind it The fourth set passes from one rib over the next, and is inserted into the second rib. The fifth set goes from rib to rib. On the inside of the chest there is a strong set of muscles attached to the anterior snrface of each vertebra, and passing obliquely forwards over four ribs to be inserted into the fifth, nearly at the middle part between the two extremities. From this part of each rib a strong flat muscle comes forward on each side before the viscera, forming the abdominal miracles, and uniting in a beautiful middle tendon, eo that the lower half of each rib which is beyond the origin of this muscle, and which is only laterally oonnected to it by loose cellular membrane, is external to the belly of the animal, and is used for the purpose of progressive motion ; while that half of each rib next the spine, as far as the lungs extend, is employed in respiration. At the termination of each rib is a small cartilage in shape corresponding to the rib, only tapering to the point Those of the opposite ribs have no connection, and when the ribs are drawn outwards by the muscles, they are separated to some distance, and rest through their whole length on the inner surface of the abdominal acute, to which they are connected by a set of short muscles ; they have also at connection with the cartilages of the neighbouring ribs by a rad of short straight muscles. These observations apply to snakes in general, but the mullein have been examined in a Boa Constrictor 3 feet 9 inches long preserved in the Hunterian Museum. In all snakes, adds the author, the ribs are continued to the anus, but the lungs seldom occupy more than one half of the extent of the cavity covered by the ribs. C<' in eminently these lower ribs can only be employed for the purpose of progressive motion, and therefore correspond in that respect with the ribs In the Dram colons euperadded to form the wings.