VESTIGIAL STRUCTURES. 93 
animals, it may be useful to draw attention to one con- 
dition, indirectly associated with this remarkable change, 
which produces greater inconvenience than can be attri- 
buted to cervical auricles. In many of the situations 
where canals open on a free surface, the terminal orifice 
of the canal is, as a rule, surrounded with glands and a 
collection of tissue, peculiar in structure, termed adenoid. 
Such glandular collections are more abundant around 
the terminations of functionless ducts. Some of the 
more characteristic examples occur in the pharynx 
marking the inner orifices of the branchial clefts. Of 
these the most conspicuous is named the tonsil. 
The tonsils are familiar to all as the sub-globular 
shaped structures lodged in the recesses on each side of 
the mouth at the spot where the mouth joins the 
pharynx, or cavity where the nasal and buccal passages 
become directly continuous. The space between the 
mouth and pharynx is technically termed the fauces. 
The tonsils vary considerably in size ; in some persons 
they are large and prominent, in others small and 
scarcely recognizable. Structurally they are composed 
of adenoid tissue, covered with mucous membrane, beset 
with a number of shallow crypts which secrete thick, 
tenacious mucus. The niche in which each tonsil is 
lodged is termed the tonsillar recess, and indicates the 
exact spot where the second branchial cleft in the 
embryo communicated with the pharynx; it is also the 
spot where the cleft, when persistent, opens internally. 
The connection of the tonsil and its recess with the 
second branchial cleft is also indicated anatomically by 
the glossopharyngeal nerve and the lingual artery, 
which, in the embryo, are distributed to this cleft. 
