DEGLUTITION. 129 



The passage of the food along the throat is facilitated by 

 the mucous secretions, which are poured out from a multi- 

 tude of glands interspersed over the whole surface of the 

 membrane lining that passage. The Camel, which is formed 

 for traversing dry and sandy deserts, where the atmosphere 

 as well as the soil is parched, is specially provided with a 

 glandular cavity placed behind the palate, and which fur- 

 nishes a fluid for the express purpose of moistening and lu- 

 bricating the throat. 



In the structure of the (Esophagus, which is the name of 

 the tube along which the food passes from the mouth to the 

 stomach, we may trace a similar adaptation to the particular 

 kind of food taken in by the animal. When it is swallowed 

 entire, or but little changed, the oesophagus is a very wide 

 canal, admitting of great dilatation. This is the case with 

 many carnivorous birds, especially those that feed on fishes, 

 where its great capacity enables it to hold, for a considera- 

 ble time, the large fish which are swallowed entire, and 

 which could not conveniently be admitted into the stomach. 

 Blumenbach relates that a sea-gull, which he kept alive for 

 many years, could swallow bones of three or four inches in. 

 length, so that only their lower ends reached the stomach, 

 and were digested, while their upper ends projected into the 

 oesophagus, and descended gradually, in proportion as the 

 former were dissolved. Serpents, which swallow animals 

 larger than themselves, have, of course, the oesophagus, as 

 well as the throat, capable of great dilatation, and the food 

 occupies a long time in passing through it, before it reaches 

 the digesting cavity. The turtle has also a capacious oeso- 

 phagus, the inner coat of which is beset with numerous firm 

 and sharp processes, having their points directed towards 

 the stomach; these are evidently intended to prevent the re- 

 turn of the food into the mouth. Grazing quadrupeds, who, 

 while they eat, carry their heads close to the ground, have 

 a long oesophagus, with thick muscular coats, capable of ex- 

 erting considerable power in propelling the food in the di- 

 rection of the stomach, which is contrary to that of gravity. 



VOL. II. 17 



