158 THE VITAL FUNCTIONS. 



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 furnishes a fluid for the express purpose 

 of moistening and lubricating 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 en- 

 ables it to hold, for a considerable 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 oesopha- 

 gus, 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 digest- 

 ing cavity. The turtle has also a capacious oeso- 

 phagus, the inner coat of which is beset with nu- 

 merous firm and sharp processes, having their 

 points directed towards the stomach : these are evi- 



* Ciliary motions have been distinctly observed by Purkinje and 

 Valentin in the mouth, throat, and oesophagus of the Batrachia. 



