REPTILES. 



in truth be faid to fly: its lateral membranes aft like a 

 parachute, and e\iuble it to take long leaps. 



The ribs are iilually articulated to the vertebrx by 

 means of a convex lurfaee, which moves upon a (lightly 

 concave one formed in two of the vertebrie ; lo that the 

 hollow receiving each rib is fituatcd between two vertebra; 

 of the back. But in the fnakc tribe the head of the rib 

 has two flightly concave furfaces, which move upon a con- 

 vex protuberance b.longing to each vertebra ; fo that the 

 rib rells on a fingle vertebra. The confequence of this 

 peculiarity is, that the ribs do not interfere with the motions 

 of the individual vertebra, and thus that the latter are 

 left free to execute thole movements on each other, which 

 take place fo extenfively in the progreflion of ferpents. 

 The articulations of the vertebra; to each other, and to the 

 ribs, are reprefented of the natural fize from the Ikeleton of 

 a large boa, in the Philof. Tranf. i8l2, pt. i. pi. 6. 



We have already feen the ribs, inllead of contributing 

 to the bufinefs of refpiratici, employed for purpofes 

 of locomotion in the draco volaiis. They are Hill more 

 extenfively employed for the fame purpofe in the ferpent 

 tribe, in which they amount lomctimes to 250 pairs, as ob- 

 ferved by fir Everard Hume. Thefe bones, in all fnakes, 

 are continued to the anus, while the lungs feldom occupy 

 more than one-half the cavity covered by the ribs. The 

 hind ribs can only be employed for the purpofe of pro- 

 greffive motion, and thus corrclpond to the elongated ribs 

 of the lateral membranes in the draco volans. 



The ribs of a fnake may be feen to move forwards fuc- 

 ceflively when the animal is in motion, like the feet of a 

 caterpillar, and the ends of thefe bones can be diitinftly 

 felt on the palm of the hand, as the animal pafles over it. 



At the termination of each rib is a fmall cartilage in 

 (hape correfponding to the rib, only tapering to the point. 

 Thofe of the oppofite ribs have no connexion, and when 

 the ribs are drawn outwards by the mufcles, are feparated 

 to fome diftance, and reft through their whole length on 

 the inner furface of the abdominal fcuta, to which they 

 are connefled by a fet of iliort mufcles : they have alfo a 

 conneftion with thofe of the neighbouring ribs by a fet of 

 fhort ftraight mufcles. 



When the fnake is going to put itfelf in motion, the ribs 

 of the oppofite fides are drawn apart trom each other, and 

 the fmall cartilages at the ends of thcin are bent upon the 

 upper furfaces of the abdominal fcuta, upon which the 

 ends of the ribs i-eft ; and as the ribs move in pairs, the 

 fcutum under each pair is carried along with it. This 

 fcutum, by its pofterior edge, lays hold of the ground, 

 and becomes a fixed point, from whence to fet out anew. 

 This motion is beautifully feen, when a fnake is climbing 

 over an angle, to get upon a flat iurface. 



The coluber and boa, having larger abdominal fcuta, 

 which may be confidered as hoofs or (hoes, are the beft 

 fitted for this kind of progrellive motion ; there is, however, a 

 futiilar t\rufture of ribs and mufcles in the anguis and am- 

 phifbiiena. In the anguis the ribs are proportionally weaker, 

 and as thefe have nothing to correlpond to the fcuta, this 

 mode of progrellive motion is probably lels neceliary to 

 them. See " Obfervations intended to (hew that the pro- 

 grcffive Motion of Snakes is partly performed by means of 

 the Ribs," by fir Everard Hume, Philof. Tranlaft. 1812, 

 pt. 1. pag. 183, with figui-es. We are alfo indebted to 

 fir Everard Hume, in conjunftion with Dr. Rufiel, for 

 defcribing more particularly a facl; noticed by Bhimeiibach, 

 ^Comp. Anat. p. 117.), viz. an adaptation of certain 

 ribs in the cobra de capello (coluber iiaia, L.) to the ac- 

 «omph(hmeiit of a particular mechanifm in that animal. 



This ferpent is called the hooded fnake, from a power of 

 expanding the Han of the neck, which is effefted by thf 

 motions of tlie ribs. In other ferpents, the ribs, from the 

 firft vertebra to thofe of the middle of the trunk, gra- 

 dually increafe in length ; thence they gradi:ally (horten 

 or decline, to near the end of the tail, where they difap- 

 pear, or are transformed into fliort eminences. In the 

 naia, the cervical ribs gradually lengthen to the tenth or 

 eleventh, after which they fucccfiivcly (horten to the 

 twentieth. Again increafing in length, they are, at the 

 middle of the trunk, nearly as long as the middle cervical 

 ribs, and then declining as in other ferpents, difappear on 

 the tail. 



The firft twenty ribs, inllead of bending equally with 

 the others towards the belly, go out in a lateral dircftion, 

 having only a (light curvature, and when deprelTed lie at 

 the fide of the fpine upon one another. The firil is fliorteit • 

 they lengthen to the tenth, and are again (hortened to the 

 twentieth; fo that, when they are extended, they ivprefent 

 an oval figure, ef which the fpine is the middle line or long 

 axis. In the extended ftate of the ribs, the (kin of the 

 back is brought over them, forming the hood ; and in their 

 deprefi'cd ftate it recedes. From the rounded form of the 

 hood, the (I'cin has the appearance of being inflated ; but 

 the moft careful examination did not difcover any commu- 

 nication between the trachea or the lungs and the cellular 

 membrane under the ficin. See " Remarks on the voluntary 

 Exponfion of the Skin of the Neck in the Cobra de Ca- 

 pello," &c. by Pat. Rud'el, M.D. and Everard Hume, efq. 

 Philof. Tranf. 1804, pt. 2. pag. 346. 



The exiftence of ribs has been denied in the firen lacer- 

 tina, and proteus anguinus : they have in truth merely 

 very infignificant rudiments of ribs, that might be eafily 

 ovcrlooked. Thefe have nothing to do with the refpiration 

 of the animals, indeed they are too fmall to anfwer any 

 purpofe. See the defcription of thefe animals at the end of 

 the prefent article. 



Such rudiments of ribs are faid to exift in the genus 

 caecilia, among ferpents. 



Bones of the Shoulder. — In oviparous quadrupeds the gle- 

 noid cavity of the flioulder is partly compofed of the fcapula, 

 and partly 6/" Mf c/aOTi;/?. The fcapula, which is elongated, 

 has no fpine ; it contrafts and becomes thicker towards 

 the neck. The clavicle is fimple, ftiort, and flat, and united 

 to the fternum in the crocodile and lizards. It is broad, 

 and almoft fq.iare, in the iguana and cameleon ; in the tupi- 

 nambis it is oval, and very large and long between the front 

 and back, and has two un-olTified parts. The frog and toad 

 have two clavicles to each fhoulder, attached to the two ex- 

 tremities of the ilcrnum. The fcapula is bent, and com- 

 pofed of two articulated pieces, with the fuperior ene in- 

 clined towards the fpine. The fame conformation obtains 

 in the Surinam toad.' The anterior clavicles appear to cor- 

 refpond to the os furciforme of birds. The clavicle, the 

 iternum, and the firft piece of the fcapula, are anchylofed 

 together. The falamanders have the (houlder formed in a 

 moft fingular manner, the fcapula, clavicle, and iternum, 

 confift only of a fingle bone, which receives the head of 

 the humerus. The (houlder is almoft all cartilaginous, but 

 the part anfweriiig to the fcapula is more diftinCt than the 

 relt. It inclines towards tlie fpine, where it receives the 

 mulcles by which it is moved. The clavicular part is direfted 

 towards the head; that which fupplies the place of the 

 ileraium turns towards the breaft, but without uniting with 

 the bone of the oppofite fide ; the part on the right fide 

 Aides over that on the left. This conformation allows a 

 greater dilatation of the breaft in refpiration. The lortoife 



has 





