SERPENTS. 403 



partly in the peculiar conformation of the ribs. 

 The edges of the scales form rough projections, 

 which are directed backwards, so as to catch the 

 surfaces of the bodies to which they are applied, 

 and to prevent any retrograde motion. In some 

 species the integument is formed into annular 

 plates, reminding us of the structures so prevalent 

 among worms and myriapode animals. Each scale 

 is connected with a particular set of muscular 

 fibres, capable of raising or depressing it, so that 

 in this way it is converted into a kind of toe ; and 

 thus the body rests on the ground by numerous 

 fixed points of support. 



This support is farther strengthened by the con- 

 nexion of the ribs with the abdominal scuta, or the 

 scales on the under side of the body. The mode 

 in which the ribs become auxiliary instruments of 

 progressive motion was first noticed by Sir Joseph 

 Banks.* Whilst he was watching the movements 

 of a Coluber of unusual size, which was exhibited in 

 London, and was moving briskly along the carpet, 

 he thought he saw the ribs come forward in suc- 

 cession, like the feet of a caterpillar. Sir Everard 

 Home, to whom Sir Joseph Banks pointed out this 

 circumstance, verified the fact by applying his 

 hand below the serpent, and he then distinctly felt 

 the ends of the ribs moving upon the palm, as the 

 animal passed over it. The mode in which the 

 ribs are articulated with the spine is peculiar, and 

 has evidently been employed with reference to this 

 particular function of the ribs, which here stand in 

 place of the anterior and posterior extremities, pos- 



* Philos. Trans, for 1812, p. 163. 



