The subjoined cut, copied from that given as an illustration by Sir Everard Home, will explain the articulating surfaces of the vertebra) and ribs; and on the under surface of the former will be soon the protuberance for the attachment of the muscles which are employed in crushing tho animals round which the snake entwines itself.
The cut exhibits two vertebra, and portions of two ribs of a so called Boa Constrictor, drawn from a skeleton eent from the East Indies by the late Sir William Jones, and deposited in the Hunterian Museum. The letters, a, a, point to the protuberance on the under surface for the attachment of the constricting muscles, according to Sir Everard Home.
Though the term Boa Constrictor is used throughout by Sir Everarti home in his lecture, there can be little doubt that the serpent pent from India by Sir William Jones was a Python. The small specimen from which the description of the organs employed in progressive motion was taken may have been a boa. But whether boa or python, it would have had the hooks or spurs near the vent, and the bones and muscles belonging to these spurs, which are of no small consequence in the organisation of a boa or a python, rudiments of limbs though they be ; these appear to have escaped Sir Everard Home's observation, occupied as he was in following out the mechanism of progressive motion.
No one can read of the habits of these reptiles in a state of nature without perceiving the advantage which they gain when holding on by their tails on a tree, their heads and bodies in ambush, and half floating on some sedgy river, they surprise the thirsty animal that seeks the stream. These hooks help the serpent to maintain a fixed point ; they become a fulcrum which gives a double power to his energies. Dr. Mayor detected these rudiments of limbs, and has well explained their anatomy. Ile says that the spur or nail on each side of the vent in the Boa Constrictor and other species of the genus is a true nail, in the cavity of which is a little demi-cartilaginous bone, or. ungual phalanx, articulated with another bone much stronger which is concealed under the skin. This second bone of the rudiment of a foot in the Boa has an external thick condyle, with which the ungual phalanx is articulated, as above stated ; it presents, besides a smaller internal apophysis, which places it in connection with the other bones of the skeleton. These bones are the appendages of a tibia, or leg
bone, the form and relative position of which will be understood by a reference to the subjoined cuts, copied from Dr. Mayer's Memoir.' (' Trans. Soc. Nat. Curios.; translated in Annales des Sciences' for 1826.) The previous figure represents the tail of a Boa Constrictor ; a, the vent ; b, the hook or spur of the left side ; c, the subcutaneous muscle ; d, ribs and intercostal muscles ; e, transverse muscle of the abdomen; f, bone of the leg enveloped in its muscles ; g, abductor muscle of the foot; lt, adductor muscle of the foot. The arrange ment of the senta, or shields, of one entire piece under the tail, characteristic of the true Boas, will be here observed. In the Pythons the shields beneath the tail are ranged in pairs.
We here have a representation of the osteology of this rudimen tary limb, taken from the same author. Fig. 1 represents the left posterior limb of the Boa Scytale, seen anteriorly : a, tibia, or leg-bone; b, external bone of the tarsus; c, internal bone of the tarsus; d, bone of the metatarsus with its apophysis; e, nail or hook.
Fig. 2 represents the same limb, seen pos teriorly.
Doctors Hopkinson and Pancoast have given in the Transactions of the American Philoso phical Society,' held at Philadelphia, for promoting useful knowledge (vol. v. new series, part i.), an interesting account of the visceral anatomy of the Python (Cuvier), described by Daudin as the Boa ret ieulata. And here it may be as well to remark that the differences between the Boas and the Pythons are so small, that the accounts given of the constricting powers and even of the principal anatomical details of the one, may be taken as illustrative of the same points in the history of the other.
Perhaps the best way of illustrating the habits of these creatures in seizing and killing their prey is to relate some of the incidents with which books of travels abound.