MUSCLES OF THE LARYNX. 
451 
nearer together than they are found to be in a state of inaction, 
and that is the arytenoid muscle. They cover the posterior part 
of the arytenoid cartilage,—arising on either side from the spine 
of the arytenoid cartilage,—occupying the whole of the posterior 
surface of that spine, filling the depression at the base of it; 
diminishing in width as the cartilage diminishes ; in the centre, 
where the cartilages are connected together by cellular mem¬ 
brane, becoming thinner, and exhibiting many tendinous fibres; 
enlarging again with the enlargement of the cartilage on the 
other side, and so extending from the spine of one of the carti¬ 
lages to that of the other, and occupying, as I have said, the 
whole of their posterior surface. 
The function of this muscle is immediately evident; it presses 
the arytenoid cartilages nearer together, and so closes the aper¬ 
ture between them, and also that between the vocal ligaments. 
It is a muscle of no great power, but it is sufficient for the pur¬ 
pose. It is an antagonist to all the dilators, and it effects the 
farther object of contracting these apertures even within their 
natural dimensions. 
The Thyro-arytenoideus. —This is a very short pair of muscles, 
extending from the middle of the inside of the posterior edge of 
the thyroid cartilage to the arytenoid muscles, among the fibres 
of which it is lost. Its function is to approximate the thyroid 
and cricoid cartilages, and to limit the action of the arytenoideus 
muscle. 
The Thyro-epiglottideus .—This is a pair of somewhat expanded 
but thin muscles, climbing up the inside of the thyroid cartilage, 
and, opposite to the hyo-thyroideus, inserted into the base 
of the epiglottis, which is thickened, and tuberculated, and 
roughened for the purpose. They are weak muscles, and act at 
mechanical disadvantage. They assist in depressing the epi¬ 
glottis, in order to cover the aperture into the larynx. 
The Aryteno-epiglottideus is another pair of small muscles, 
running from the lower and anterior angle of the arytenoid car¬ 
tilage to the slips of cartilage at the base of the epiglottis. 
Their action is doubtful ; they seem to contribute to the support 
of the epiglottis, by connecting it more with the other cartilages, 
and keeping it steady in the extensive motion which it undergoes 
when closing the aperture into the trachea. 
Other Muscles common to other parts •—These are all the 
muscles peculiar to the larynx. But there are others connected 
also with other parts which have considerable influence in the 
proper performance of the functions of the larynx. The hyo- 
thyroideus was described, in the 15th lecture, arising from the 
whole of the inferior border of the body of the os hyoides, ex- 
