48 STRUCTURE AND ECONOMY OF THE HORSE. 



the bronchi connected with them, and an infinite number of 

 arteries, veins, and absorbent vessels, the whole being connected 

 together by cellular membrane, thus forming these light, spongy, 

 yet important bodies, which closely packed away in the cavity 

 of the chest, exactly accord to it in shape and size. 



The upper part of the windpipe is connected wnth the mouth 

 by means of a strong cartilaginous box, termed the Larynx, 

 which is composed of five cartilages, the thyroid, the cricoid, the 

 two arytenoid, and the epiglottis.* The Thyroid is the largest 

 of the five, and is so called from its resembling, and acting as a 

 shield. It forms the front part of the lai'ynx and great portion 

 of its sides, and consists of two parts, the upper of which is con- 

 tinuous, but the sides of the lower recede so as to form a trian- 

 gular space, which is occupied by a ligament. 



The Cricoid, or ring-like cartilage, is placed below the thyroid. 

 Its anterior portion resembles a ring of the windpipe, but its 

 back part is considerably broader, so that it overlaps the first 

 ring of the trachea, somewhat in the form of a helmet. 



The two Arytenoid, or ewer-shaped cartilages, are much smaller 

 than the other, and are placed at the upper part of the larynx, 

 immediately adjoining the back part of the cricoid ; thus placed, 

 these triangular bodies leave an aperture between them, which' 

 forms the entrance to the windpipe, and their margins are 

 covered by a membrane, which forms what is called the Rima- 

 ylottis. 



The fifth cartilage is called the Epiylottis, so termed from its 

 office, which consists of shutting down upon the glottis like the 

 lid of a tea-pot, to which, from its heart-like shape, it is ad- 

 mirably adapted. Viewing this cartilage in its usual position, 

 we find that its surface nearest the larynx is smooth and some- 

 what convex, whilst that portion nearest the mouth presents a 

 concave surface. 



The larynx is lined throughout its internal surface by a fine 

 delicate membrane, which secretes a mucus for its protection. 

 It is also abundantly supplied with nerves, by which it is ren- 

 dered peculiarly sensible, and in this respect greatly differs from 

 the membrane lining the windpipe ; for whilst the latter may be 

 scratched with impunity after the operation of tracheotomy, the 

 slightest intrusion of a foreign body on the former produces the 

 most immediate and violent coughing, thus expelling the in- 

 truding body. 



The glottis, thus constituted, is admirably adapted for guard- 

 ing the entrance to the windpipe, and, generally speaking, a 

 cough arises from some irritation of this part. 



* A cut representing the various cartilages of the windpipe will be found 

 in the chaiiter on Roaring. 



