448 MR. youatt’s veterinary lectures. 
is, however, difficult to establish a perfect separation between 
them. 
They evidently possess great power, for they are thick, and 
many tendinous fibres mingle in their composition; but, inserted 
at the very base of the arytenoid spine, they act with considera¬ 
ble mechanical disadvantage. Adhering throughout the whole 
of their development to the cricoid cartilage, their action must 
be very limited. Their function is evident—to elevate and to 
draw backward the arytenoid cartilages; but, acting upon them 
in an oblique direction, these cartilages are opened while they 
are raised. The glottis is also dilated, and the vocal ligaments 
tightened. 
This muscle is not so large or so powerful in the ox. In the 
swine it is more powerful, and has a greater proportion of ten¬ 
dinous substance in its composition. 
The Crico-thyroideus. —Placed laterally at the base of the 
larynx on each side, occupying the whole of the side of the cri¬ 
coid cartilage, and filling the depression in it, and also attached 
to the side of the base of the thyroid cartilage, from the inferior 
corner posteriorly to the interposed ligament between the alae of 
the cartilage anteriorly, and running along the hoop of the cricoid 
ring, yet more anteriorly, is the crico-thvroid muscle. It ap¬ 
proximates or brings together the two cartilages, or, according as 
either of them is considered to be or made the fixed point, it de¬ 
presses the thyroid or elevates the cricoid; and, in either case, sepa¬ 
rates the arytenoid cartilages and relaxes the vocal ligaments. The 
trachea itself is also shortened by the action of this muscle, and 
thus the voice is, in some degree, affected. This muscle is also 
of small size in the ox, and more developed in the hog. 
The Crico-arytenoideus Lateralis. —In order to bring the next 
muscle belonging to the cricoid cartilage fully into view, we must 
detach one side of the thyroid cartilage ; and there, inserted into 
the anterior side of the tubercle at the base of the spine of the 
arytenoid cartilage, and arising from the upper edge of the side 
of the cricoid cartilage, and extending as far as the interposed 
ligament of the thyroid cartilage, is the lateral crico-arytenoid 
muscle. This is, in some measure, an adjuvant to the crico-ary¬ 
tenoid, and also an evident antagonist to its too powerful action. 
By drawing forward the base of the arytenoid cartilages, it brings 
forwards and elevates the upper part of them, and thus separates 
them, and also dilates the rimae glottidis, and relaxes the vocal 
ligaments. 
And now, having this portion of the larynx under the thyroid 
cartilage exposed, w*e will examine the other muscles which are 
here brought into view. I use the term in the plural number, 
