82 



NOTES. 



NOTES. 



On Deglutition in the Fresh-water Snake. — In some snakes, 

 notably in the constrictors, the process of deglution has been 

 watched, the means accounted for ; but I do not find that any 

 record of the mode of swallowing in our fresh-water snake, 

 Tropidonotns picturatus, has hitherto been made. It is indeed 

 hardly probable that this reptile has ever fed under close 

 observation, it may therefore add a mite to the sum of know- 

 ledge if we make use of opportunities afforded by an individual 

 in captivity to render an account of it. It differs much, I may 

 say essentially, from that natural to the constricting snakes. 

 In the Boas and Pythons the process is said to be wholly 

 dependent on the action of the jaws. They consist of six 

 longtitudinal arches of bone closely beset with backwardly 

 curved teeth, one pair forming the edges of the upper jaw, 

 another pair the palate, the third the lower jaw, all loosely 

 connected and each served by muscles of its own, capable 

 of pulling it forward or backwards. The snake having taken 

 its lifeless victim in its gape prepares to swallow it, unfixes 

 one of its six jaws ,and pushing it forward a little refixes 

 it, then releases the next jaw and carries it forward, thus it 

 puts in motion the whole of its jaws in succession, the first still 

 advancing as the others follow : the result obviously being that 

 in the woids of our authority, Professor Owen, ' by their succes- 

 sive movements the prey is slowly and spirally introduced into 

 the wide gullet.' But careful observation has so far failed to 

 detect similar movements of the jaws in the fresh-water snake. 

 Seizing a frog by any part of the body it proceeds at once to 

 swallow it alive and it is in the neck that the first movement to 

 that end is perceived : commencing at the head on one side it 

 is seen to rise rapidly forward step by step, while on the other 

 side it is falling similarly backwards. The purpose seems to be 

 that of suction. By the frequent repetition of the act the 

 prey is drawn in to a slight degree and then the advantage 

 obtained is secured by the simultaneous advance of the jaws on 

 the body of the victim : thus little by little the prey dis- 

 appears in a straight line inwards. As soon, however, as a 

 sufficient surface of its body has passed beyond the jaws it is 

 subjected to the direct application to it of the muscular walls 

 of the neck, and it is carried or rather stroked downwards more 

 actively if not more expeditiously. The muscular movements 



