CONTRIBUTIONS TO ZOOLOGICAL ANATOMY. 595 
The Genio-hyo-glossns, forming the central muscle of the tongue, 
is thin and triangular, narrow and pointed at its origin from the 
lower jaw, and radiated towards its insertion. It arises from the 
concavity of the symphysis menti, immediately in front of the 
genio-hyoideus, and, becoming radiated, it is inserted into the 
whole length of the tongue, from the tip to its base, and also into 
the body and anterior cornu of the os hyoides. 
Externally it is covered by the anglo-hyoideus, the stylo-glossus 
longus and brevis, the hyo-glossus, and the apex of the styloid ap- 
pendage of the temporal bone, the sublingual gland, and the gusta- 
tory branch of the fifth pair of nerves. Internally it lies in apposi- 
tion with the opposite genio-hyo-glossus, and posteriorly its hvoi- 
deal fibres arch over the concave edge of the anterior chondro- 
hyoideus. In its action it produces several of the movements of 
the tongue. When it is fixed and pointed by the other muscles, 
the posterior fibres carry it out of the mouth, and the anterior set 
will afterwards restore it to its usual position. The whole length 
of the muscle acting along the centre, will render it concave along 
the mesial line, and form a channel for the safe passage of the 
liquid part of the food to the pharynx. 
When we look, therefore, to the various movements of the organ 
in the graminivora, the herbivora, and the carnivora, we find them 
very numerous and complicated. On anatysing them, however, 
we find that they may be arranged under the elementary forms of 
protrusion, retraction, depression of the centre and of the tip; ele- 
vation of the tip, and lateral inclination of the whole. The mus- 
cles, therefore, that induce these different movements maybe thus 
classified : — Protrusion is effected by the genio-hyo-glossi, and 
these with the hyo-glossi and stylo-glossi breves again produce 
Retraction. Depression of the centre is the result of the combined 
actions of the middle fibres of the genio-hyo-glossi, the hyo-glossi, 
and the stylo-glossi breves muscles. Depression of the tip is 
caused by the contraction of the anterior fibres of the genio-hyo- 
glossi : elevation of the tip by the stylo-glossi longi, and lateral 
inclination of it , so as the whiskers may be cleaned, food grasped, 
or the cheek pouches emptied by the stylo-glossi longi and breves 
and the hyo-glossi muscles. Compression and elevation of the 
base towards the mouth is caused by the anterior chondro-hyoideus; 
and retraction of the base and passive depression of the epiglottic 
fibro -cartilage on the anterior aperture of the larynx is completed 
by the action of the posterior chondro-hyoidei. 
The Lingualis muscle is the term applied to a series of irregular 
bands and lamellse of muscular fibres placed chiefly immediately 
beneath the dermo-mucous membrane of the tongue. 
