78 EVOLUTION AND DISEASE. 
organ to indicate its previous existence. A careful 
inquiry will reveal the occasional presence in the 
tongue of a duct passing from the hyoid bone to the 
foramen cecum. This is not a duct which requires a 
microscope to distinguish it, but is capable of admitting 
a bristle or fine probe. In some cases this duct becomes 
obstructed at the upper opening, and the gradual accu- 
mulation in its interior of shed epithelium and sebace- 
ous matter gradually distends into a large and trouble- 
some cyst. In some cases the walls of the cyst are 
formed of skin, and hair may sprout from it. These 
cysts are not infrequent in the human subject, and have 
been found occupying the centre of an ox tongue, under 
rather unpleasant circumstances. A gentleman, whilst 
carving a tongue at breakfast, unexpectedly came upon 
a collection of hairs and fatty material in its midst, and 
was in no small measure astonished. 
The mammalian tongue should be an organ of great 
interest to the morphologist ; unfortunately its evolu- 
tion has not yet been thoroughly unravelled. It has 
of course received great attention from anatomists and 
surgeons. From anatomical and pathological stand- 
points the anterior two-thirds of the tongue differ com- 
pletely from the posterior third. The latter part may 
be regarded as the more primitive, whilst the tip of the 
tongue is of later development and, morphologically, 
less important. 
