BOID.E. 



r.i.ii'.r. 



Before entering upon the subdivisions of thin family we will examine 

 some of the most remarkable point* in the structure and organisation 



On looking at the accompanying representation of the skeleton of a 

 Bo Coiutrirlor, drawn from the beautiful preparation in the British 

 Museum, we first observe the strong close-set teeth, of which there 

 is a double row on each side of the upper jaw, all pointing backwards, 

 and riving the serpent the firmest hold of its struggling victim, 

 which is thus deprived of the power of withdrawing itself when once 

 looked within the deadly jaws. Serpents do not masticate. The prey 

 i> swallowed whole, ana to assist deglutition their under jaw consists 

 of two bones easily separable at the symphysis, 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 scuta, 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 are drawn apart from each other, and the small 

 cartilages at the end of them are bent upon the upper surfaces of the 

 abdominal scuta 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 scuta, which may be considered as hoofs or 

 shoes, are the best fitted for this kind of progressive motion." (' Lec- 

 tures on Comparative Anatomy,' vol. i.) 



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 locomotive power of the ribs of the Boa. 



Sir Everard Home informs us by what additional mechanism this 

 faculty is effected. The ribs, he observes, are not articulated in snakes 

 between the vertebrae, 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 surface 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 muscles, and uniting in a beautiful middle ten- 1 

 that the lower hall* of each rib which is beyond the origin of this 

 muscle, and which is only laterally qonnected to it by loose cellular 

 membrane, is external to the belly orthe 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 



length on the inner surface of the abdominal scuta, to which they are 

 connected by a set of short muscles ; they have also a connection with 

 the cartilages of the neighbouring ribs by a set of short straight 

 muscles. These observations apply to snakes in general, but the 

 muscles have been examined in a Baa Corulrictor 3 feet '.) 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, 

 soquently these lower ribs can only be employed for the purpose of 

 progressive motion, and therefore correspond in that respect witli 

 the ribs in the Draco rokuu superaddeil t form the wings. 



The subjoined cut, copied from that given as an illustration by Sir 

 Everard Home, will explain the articulating surfaces of the vertebrae 

 and ribs ; and on the under surface of the former will be seen the 

 protuberance for the attachment of the muscles which are employed 

 in crushing the animals round which the snake entwines itself. 



The cut exhibits two vertebra), and portions of twu rilw of a so- 

 called Boa Constrictor, drawn from a skeleton sent from I li-- K:i-t Imlir-i 

 by the late Sir William Jones, and deposited in the Hunterinu MUMMIHI. 

 The letters, o, 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 Everard 

 Home in his lecture, there can be little doubt that the serpent 

 from Iniliu by Sir William Jones was a Python. The small s|x 

 from which the description of the organs employed in progressive 

 motion waa 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 observat ion, 

 occupied as he waa 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 whrn h' ilding 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 ili.it 

 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. MMUT detected these niilimrnts of limb-. n<l lia< well 

 explained their anatomy. He Bays that thr spur or nail mi IM. 

 of the vent in the Boa Comtrirtm- ami otln-r spn \<-~ -if thr t" " 

 I true noil, in the cavity of which is a little demi-cartilai;iiiouH bone, or- 

 , ungual phalanx, articulated with another bone much stronger which 



