VESTIGIAL STRUCTURES. 95 
It has already been mentioned that they communicate 
with the nasal chambers by slit-like orifices; conse- 
quently, when a horse sniffs, air is drawn into the 
pouches. Should this occur when horses are feeding in 
a manger or nosebag, and the food is dusty, irritant 
particles of dust are drawn into the guttural pouches 
and set up inflammation. Dust and mucus thus ac- 
cumulating in the sac give rise to rounded bodies, 
Fic. 49.—Concretions from the guttural pouches of the Horse. 
One is shown in section. (Natural size.) 
technically known as concretions from the guttural 
pouches. Sometimes they are oval, sometimes bean- 
shaped, and vary in size from a cherry-stone to a walnut, 
and in number from three or four to a hundred, Their 
consistence resembles cheese, and on section exhibit a 
laminated structure (fig. 49). 
