94 E VOL UTION AND DISEASE. 



How far the tonsil subserves any useful purpose is 

 very doubtful : certainly they are often removed, and 

 persons usually experience relief rather than suffer 

 inconvenience from the loss. Of course they are only 

 removed when enlarged from disease ; and it is quite 

 certain that the tonsils are often the seat of disease 

 which is not merely troublesome to the individual, but 

 is at times fraught with great danger to life. 



The anatomy of this region in the horse is instructive. 

 In this mammal veterinarians describe the tonsil as 

 absent. In that the horse has no collections of adenoid 

 tissue in the sides of the fauces such as exist in man, 

 the statement is correct ; but we find on each side a 

 large cyst occupying the pharynx and constituting a 

 chamber of communication between each eustachian 

 tube and the nose. These large sacs are known as the 

 guttural or eustachian pouches. A careful study of 

 these pouches has induced me to regard them as dilata- 

 tions of the pharyngeal ends of the second branchial 

 clefts ; these are the clefts from which the tonsils of 

 man arise. It is also of some importance to remember 

 that in the early human embryo the tonsil is represented 

 as a sac with a slit-like opening wherewith it communi- 

 cates with the pharynx. The connection of the guttural 

 pouches with the eustachian tubes is secondary. 



It is not my intention to enter in detail into the 

 structure and relation of these curious pouches ; but to 

 point out that, like the tonsils of man, they are sources 

 of inconvenience, trouble, and occasionally disaster. 

 Like the tonsils, also, no known function is served by 

 these pouches. 



