430 MR. YOUATrs VETERINARY LECTURES. 
his muzzle and his face into all manner of filth, and who, blowing 
into his food, in his peculiar manner, to stir up the very sediment 
of it, would otherwise get many an irritating and noxious sub- 
tance in his windpipe. The inferior cornu of the thyroid bone is 
comparatively more developed than in our other patients. But it 
is time to look into the the larynx. 
The Chorda Vocales .—When we look into the aperture between 
the arytenoid cartilages, we see a second mouth, or opening, into 
the trachea: it is likewise of a triangular form, stretching from 
the thyroid anteriorly, to the termination of the arytenoid car¬ 
tilages posteriorly; the apex or point being before, and the wider 
part of the angle backward. These projections consist of folds 
of the membrane lining the larynx, and particularly of the 
membrane forming the inner covering of, or opposite to, the 
middle thyro-arytenoid muscles. 
The Voice .—This membrane hangs loosely in the cavity of the 
larynx, and is put into motion by, or vibrates from, the impulse 
of the air that passes. The vibrations of the chordae vocalae, 
or vocal ligaments, are communicated to the surrounding air, and 
they spread in every direction until they reach the delicate mem¬ 
brane of the tympanum of the ear. That membrane responds to 
the motion without, and the vibration is carried on to the delicate 
expansion of the pulp of the auditory nerve, deep in the recesses 
of the ear: and so we have the sense or perception of sound. 
The quality or tone of the sound depends on the rapidity of 
these vibrations, and that is regulated by various circumstances, 
but, more than any, by the nature and size of the vibrating body. 
In a cord, and these are cords stretched across the larynx, it 
depends on the tenseness or shortness of the string, or on both 
combined. As I tighten the string of a violin, or as I shorten it, 
by running my finger down the board, I increase the number of 
the vibrations in the given time, and the acuteness of the sound ; 
and so as I tighten the chordae vocales, or diminish their length, 
I regulate the tone of the voice. The loudness of the voice 
depends on the force with which the air rushes by ; the acuteness 
of the tone, on the shortness or tension of the string. You observe 
the acute angle which the chordae vocales form ; they are in 
contact with each other at the apex or point of the angle, and 
these cartilages, which I have described, are so connected with 
each other, and furnished with so many powerful yet delicate 
muscles, that the state of the chordae is perfectly under the 
control of the will. The aperture between these vocal ligaments 
is called the rima glottidis, or opening of the glottis. By an 
effort (and if we will observe the manner in which this is effected 
in ourselves we shall be conscious of the effort) the animal can 
