ORDER OPHIDIA. 329 



but not one from which luxation might ensue, while the 

 imbricated articulations of the several vertebrae, and the ball 

 and socket junction of the ribs with the spine, enables the 

 animal to execute the various tortuous gesticulations of the 

 body of which snakes are capable. 



The muscles which act on the bony frame have also a pe- 

 culiar arrangement. There appears to be five different sets of 

 muscles which bring the ribs forward — the first of these pro- 

 ceeds from each vertebra to the head of the rib immediately 

 behind it — the second set are attached to the first and fourth 

 ribs passing over two in a slightly inclined direction — the third 

 in like manner passes over two ribs, but in a much more in- 

 clined direction, being attached to one rib near its articula- 

 tion with the spine, and to the other not far from its termi- 

 nation beneath — the fourth passes over only one rib in a 

 direction nearly parallel with the second, and the fifth or 

 undermost set pass from one rib to the next for nearly their 

 entire length. 



The forward motion is moreover considerably accelerated 

 by the scutae, or transverse plates on the abdomen, which are 

 attached on each side to the squamas or scales. These scutae 

 are connected with the ribs by the upper edge only at each 

 end, and when brought forward by the ribs, the scutae have 

 some hold on the ground by the under edge, and each be- 

 comes a sort of fulcrum to assist pi'ogression. All the five 

 sets of muscles which bring the ribs forward, act conjointly 

 on them, besides which, each pair of ribs, with their scutum, 

 has a separate motion, and hence proceeds the amazing power 

 of constriction which the boa is known to possess, as well as 

 the capability of locomotion common to the order. 



Some writers assert that the boas are found in the East 

 Indies. But our author''s opinion, as we have already seen, 

 is different, who thinks that there are no true boas in the east. 

 They are sometimes to be seen of thirty feet in length. They 



