427 
OF THE LARYNX OF THE HORSE, &C. 
base it is united to the thyroid cartilage by ligamentous sub¬ 
stance, and derives support from it; and also, springing from the 
base of the spur of the hyoid bone, a muscle, the hyo-epiglottideus, 
is found, which was described in the lecture before the last, giving 
it farther support. This muscle is not found in the human 
being. The epiglottis is placed at the extremity of the opening 
into the windpipe, with its back opposed to the pharynx, so that 
when a pellet of food passes from the pharynx in its way to the 
oesophagus, it presses down the epiglottis, and by this means 
closes the aperture of the larynx, and prevents any portion of 
the food from entering it. The food having passed over the epi¬ 
glottis, that cartilage, from its own elasticity and that of the mem¬ 
brane at its base, and more particularly the power of the hyo- 
epiglottideus muscle, rises again and resumes its former situ¬ 
ation. 
I am aware of the opinion of those who consider the epiglottis 
as connected with the voice alone—that it is a tongue of elastic 
substance placed to break the current of air, and to prevent any 
loud note from breaking into a higher tone. I have not time for 
this controversy, but acknowledge that I here belong to the old 
school, and believe that the principal use of the epiglottis is to 
close the entrance into the windpipe. Although this preserva¬ 
tion of the tone may be a subordinate function, yet it is one that 
is not perfectly discharged, for an ox will seldom low without 
“ the loud note breaking into a higher tone.” 
The Thyroid Cartilage .—Occupying almost the whole of the 
external part of the larynx, both anteriorly and laterally, is the 
thyroid cartilage. It envelopes and protects all the rest, a point 
of considerable importance, considering the injury to which the 
larynx is exposed by our cruel system of curbing and tight rein¬ 
ing : it also forms a point of attachment for the insertion of the 
greater part of the delicate muscles by which the other carti¬ 
lages are moved. It derives its name from its supposed shield¬ 
like form ; but in the horse, although it discharges the office of 
a shield, it does not bear the most distant resemblance to this 
portion of defensive armour. It consists of two alae or wings, 
forming the lateral defence of the larynx, united at the upper 
and anterior part by a knob of thick cartilage, which, at a very 
early age, becomes perfectly bony. It may be termed the head 
of the cartilage, for the wings soon widely open, and the inter¬ 
mediate space is occupied by an extensive ligament, the crico¬ 
thyroid ligament , which is attached to the anterior edges of the 
wings, and reaches down and unites with the anterior part of the 
cricoid cartilage, thus connecting together the thyroid and cri¬ 
coid cartilages. When this ligament is removed, the thyroid 
