160 TIIR HORSE. 



VVe do not require this in tlie heavy cart-horse, and we do not often find it 

 because lie is not so much exposed to those circumstances which will hurry 

 respiration, and require an enlargement in the size of the principal air-tube. 



THE LARYNX. 



At the top of the windpipe is placed the larynx, which has been partially 

 described. It is situated where from the sudden bending or motion of the 

 head it is liable to more frequent and to greater injury than the windpipe; 

 and therefore it is composed of stronger cartilages than that tube. First is 

 the thyroid, or helmet-shaped cartilage, forming the front and side parts of 

 (he larynx, and protecting the other parts of the larynx (see l,p. 68). Its 

 bulk and strength are apparent on the slightest handling. 



Immediately below the thyroid, and with its broad part behind, is the 

 cricoid, ring-like cartilage (11, p. 68). This is likewise for the purpose of 

 strength in a part so exposed to injury, but not so strong as the thyroid 

 because so much danger cannot threaten from behind. Of the epiglottis, 

 or covering of the entrance into the wind-pipe (2, p. 68), and of the aryte- 

 noid, or funnel-shaped cartilages forming that opening (3, p. 68), we have 

 already spoken. 



ROARING. 



The larynx and upper part of the Avindpipe are subject to various dis- 

 eases. The first we shall mention is Roaring ; so called from a peculiar 

 sound uttered by the horse when briskly trotted or galloped, particularly up 

 hill. In moderate exercise it is scarcely or not at all perceived, but when 

 the animal is in brisk exercise it may be heard at the distance of several 

 yards. It may easily be detected by striking the horse suddenly, or even 

 threatening him with a stick, when he will utter a singular grunt or groan. 



It is usually explained as the consequence of inflammation of the part. 

 A fluid, rapidly changes into a tough viscid substance, is thrown out, and 

 adheres to the sides of the larynx and upper part of the windpipe, materi- 

 ally obstructing the passage, and sometimes running across it in bands. 

 When the horse is blown, or his breathing much hurried, the air whistles 

 through these obstructions. We believe this to be the most general cause 

 of the disease, and a roarer is evidently unsound, for he is incapable of the 

 exertion which may not only be occasionally, but ordinarily required of him. 



Much light, however, has lately been thrown on other causes of this com- 

 plaint. Many roarers have been examined after death, and no vestige of 

 these bands have been found ; but some have had the shape of the larynx 

 and the upper part of the windpipe materially deformed, crooked and com- 

 pressed; and others have presented no appearance of disease. Then we 

 liave been compelled to look out for other causes of roaring, and some 

 very probable ones have been readily found. The parts may have been 

 subject to inflammation, and some parts of the air-tube may have become 

 thickened and inelastic. In this way the inflammation of strangles may 

 have been communicated to the larynx or windpipe, followed by some 

 alteration of structure. Roaring is no unusual consequence of strangles. 



A more frequent cause, and previously unsuspected, is tight reining. 

 There can be no doubt that many more carriage-horses become roarers, 

 than those that are used for the saddle alone ; and the explanation of thi.« 

 at once presents itself in the continued and painful pressure on these parts, 

 caused by reining in the carriage-horse, and teaching him to 'lea- himself 



