450 MR. youatt's veterinary lectures. 
can scarcely help connecting their function with that of the liga¬ 
ments. They would seem to be the moving power by which these 
ligaments are chiefly influenced. The other muscles act directly 
on the cartilages of the larynx, and only indirectly on the vocal 
ligaments; these appear to act directly upon them: they are 
bound down upon the very membrane of which these ligaments 
are a duplicature; they influence the length a^id the tenseness 
of the ligaments, and are the principal agents in effecting all 
those changes on which the character of the voice depends. 
These two muscles are not found in any other domesticated ani¬ 
mal, because there is no interposed ligament between the aim of 
the thyroid cartilage for their insertion. 
The Ligamento-arytenoideus Superior (the thyro-arytenoideus 
of Mr. Percivall and other anatomists).—This pair of muscles, 
lying above the two which I have just described, arises from the 
upper and thinner portion of the spine of the arytenoid cartilage, 
and, taking a course parallel to that of the others, is also con¬ 
nected with the lining membrane of the larynx, and with the in¬ 
terposed ligament, and at length inserted near the summit of the 
interposed ligament. This muscle may assist in the last function 
which I have attributed to the preceding ones, for it likewise is 
connected with the lining membrane of the larynx, but it is situ¬ 
ated further above the vocal ligaments : another office, however, 
is discharged, supposing the thyroid cartilage to be the fixed 
point, namely, to separate the arytenoid cartilages, and so en¬ 
large the opening into the larynx. 
The Elasticity of the Cartilages .—All these muscles are more 
or less combined in the performance of one function — the 
enlargement of the opening into the larynx, or of that between 
the vocal ligaments into the trachea. It is a very complicated 
piece of machinery, for the importance of the offices to be dis¬ 
charged would justify any intricate combination of power and 
action. There is, however, another duty to be performed—the 
bringing together again of the cartilages and ligaments, and the 
reduction of the apertures to their natural dimensions; and we 
have, in the construction of the machine, an agent so powerful 
as to require very little aid in effecting this purpose. The larynx 
is composed of cartilage, a substance highly elastic, and exhibit¬ 
ing the very perfection of elasticity. The cartilages yield to the 
force impressed upon them; but, that force removed, and the 
muscle ceasing to act, they return by their inherent elasticity to 
their natural situation and form. This principle is the antagonist 
power which stands instead of complication of muscular action. 
The Arytenoideus .—There is, however, one little muscle to 
complete the closure of these apertures, or rather to bring them 
