94 EVOLUTION 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. 
