CONTRIBUTIONS TO ZOOLOGICAL ANATOMY. 
593 
that proceed from these appendages to act with perfect energy on 
the different parts of the tongue to which they are distributed. They 
also have no influence on the condition of the anterior aperture of 
the larynx. 
Third Group. — The Intrinsic Muscles of the Tongue. 
Under this group are included those muscles that form the sub- 
stance of the tongue, and comprehends the 
Hy o-glossus. 
Stylo-glossus longus. 
Stylo-glossus brevis. 
Genio-hyo-glossus. 
Lingualis. 
In this arrangement the muscles are enumerated as they are 
observed on dissection from the side to the centre of the tongue, 
excepting, however, the lingualis, which is chiefly spread out along 
its surface. 
The Hy o-glossus is a thick, square-shaped muscle, placed ob- 
liquely along the side of the base of the tongue. It arises from 
the concavity along the side of the body and the greater part of 
the edge of the posterior cornu of the os hyoides. The fibres 
generally run in a direction vertical to the long axis of the tongue ; 
those that come from the posterior cornu pass upwards and back- 
wards to the base of the tongue ; and those from the body of the 
bone run forward to the side of the middle of the organ, where 
they become amalgamated with the substance of the genio-hyo- 
glossus, and the deep fibres of the lingualis, under cover of the 
stylo-glossus longus. None of the fibres proceed to the tip of the 
tongue, and they are seldom found beyond the elevated line on its 
dorsal surface, that separates the body from the moveable tip. 
Externally and inferiorly it is covered by the mylo-hyoideus, 
the stylo-hyoideus, the tendon of the digastricus muscles, and the 
lingual nerve ; and, internally, it lies on the lesser cornu of the os 
hyoides and the articulation between it and the apex of the styloid 
appendage of the temporal bone. Here the muscle also covers 
the lingual artery, that lies on a plane with the lingual nerve ; 
also the chondro-hyoidei, the stylo-glossus brevis, and the genio- 
hyo-glossus muscles. When the two muscles are combined in 
their action they depress the sides of the tongue, render it convex 
along the centre, and also retract it entirely within the mouth ; and 
one muscle acting alone will carry the base and body of the organ 
to its corresponding side. 
