OF S E R P E NT %. i8|, 



T he fe bones play one within another, like ball and focket, fo that they 

 have complete motion upon each other in every direiflion. From the 

 head to the vent are two ribs to every joint, ufualiy longeft in the middle 

 of the body, and capable of motion in various directions: towards the 

 end of the tail thefe ribs ceafe. They are fiirnilhed with mufcies, 

 four in number, which being inferted into the head, run along to the 

 end of the tail. The vertebrae and ribs compofe the whole foiid parts 

 of ferpents ; fo that their internal parts are defend^^d below only by the 

 fcales on which they move, and by a kind of fatty matter, which lines the 

 Ikin of their belly, often in confiderable quantities. This fat alfo con- 

 tributes to their warmth. 



Some time after the animal awakes in fpring, he acquires a new fkin, 

 and hides till it be hardened. 



Alm.oft all their fcales, but particularly thofe under the belly, which 

 contribute to motion, are moveable, independent of each other, by a 

 mufcle which belongs to each. As the edge of the foremoft lies over the 

 end of the following, when the fcale is eredted, it catches in the ground, 

 and furnifhes a point of refiflance to promote the animal's progrefiive 

 motion. It is evident that thefe fcales, lying all one way, impede, 

 or at lead: do not affift, motion the other way ; and very few ferpents 

 rriove equally well backward as forward, though fome do. In (bme of 

 the fcrpcnn kind there is the exafleft fymmetry in thefe fcales ; in others 

 they are difpofedmore irregularly. In fome there are larger fcales on the 

 belly, and often anfwering to the number of ribs ; in others, the animal is 

 v/iihout them. But ferpents have another more powerful principle of 

 rriotion, by bending into an arch more or lefs of their body ; the two 

 extremes of this arch being drawn together, one of them fcrves for a 

 point of refiflance to the other, when the arch is flraightened. At each 

 repetition of this adtion, they may be faid to nnake a leap of fuch a dif- 

 tance; and this is proportionate to the fize, &c. of the creature. During 

 this motion they carry their heads as high as they can. In comparing 

 this to vermicular motion, we obfervc, that the ear-th-worm has no back- 

 bone ; but its body is compofed of rings, which it can lengthen or 

 fliorten as necelTary : therefore, to m.ove forward, it lengthens the bo- 

 dy, and by the fore part clings to the point it has reached; then con- 

 tra<51:s, and brings up irs rear; then, the body being (hortened, the fore 

 part is lengthened again for another progreflion, and fo on : v.'hile the 

 lerpent, inftead of OiGrtcning the body, bends it into an arch; and this is 

 the principal dificrcnce between ferpencine and vermicular progreflion. 



When ' 



