420 THE HORSE. 
tributed. Each nostril has two flexible and easily dilated ale—a superior 
or internal ala, having a broad cartilaginous plate, and an inferior ala, of 
a crescentic shape, with its concavity turned inwards. The four ale, 
when in position, resemble the letter X, and form a framework which 
keeps the openings always patulous, while it resists the actions of the 
muscles when they draw the external folds of the skin away from it in 
order to enlarge the openings. ‘Two little pouches of skin are found 
internally above the true nostrils, and are called the false nostrils, the use 
of which is not known. At the inner and inferior part of the nasal fossa, 
underneath the fold of skin covering the inferior ala, is the orifice of the 
nasal duct, which leads down from the eye, and conveys the surplus 
secretion of lachrymal fluid from that organ to the nose. In the ass and 
mule this orifice is found just within the superior ala. If these ale are 
not of full size and the nostrils patulous, it may generally be surmised 
that the other organs of respiration are equally undeveloped, and that the 
horse’s wind will be proportionally bad. 
THE NASAL CAVITIES, OR FOSS, are partly bounded by bone, and partly 
by the cartilage known as the septum nasi. The surface of membrane is 
much increased by the convolutions of the turbinated bones, so that the 
air, as it passes through these chambers, is warmed if cold, and if dry it 
is moistened, so as to render it fit for respiration. The frontal, ethmoidal, 
sphenoidal, and maxillary sinuses also open into these foss, the whole 
of them being lined by a continuation of the Schneiderian membrane. 
THE LARYNX. 
IMMEDIATELY BEHIND and below the nasal cavities is the larynx, which 
serves the double purpose of acting as a portal to the inspired air, and 
of formize the few vocal sounds uttered by the horse. It consists of five 
10075 a, 
10 40 10 oom 
Fig. 6.—Prorite View of THE OS HyoipEs aND LARYNX. 
1 Lateral plates of the thyroid cartilage. 6. Spur process, or appendix. 
2. Epiglottis. 7. Short horn. 
3. Thyro-hyoid membrane. 8. Long horn of the os hyoides. 
4. Body of the thyroid cartilage. 9. 9. 9. 9. Cartilaginons rings of the trachea 
5. Branch of the body of the os hyoides. 10. 10. 10. Mentbranes connecting these rings. 
cartilages, united together by ligaments, and moved by a number of deli- 
cate muscles. It is lined with a fine mucous membrane, and is supplied, 
like all other parts of the body, by its proper vessels and nerves. It is 
suspended from the os hyoides, or bone of the tongue, by a strong but 
thin membrane, and terminates posteriorly in the trachea, or air-tube 
leading to the lungs. 
