THE PALATE — THE LARYNX. 1G3 



again to the heart, commanicate with each other by so many channels, and in such 

 various ways, that it is impossible by the closure or loss of any one of them long 

 materially to impede the flow of the vital current. If the jugular is destroyed, the 

 blood will circulate through other vessels almost as freely as before; but the horse 

 could not be considered as sound, for he might not be equal to the whole of the work, 

 required of him. 



THE PALATE — (resumed). 



At the back of the palate (see p. 72), and attached to the crescent-shaped border of 

 the palatine bone, is a dense membranous curtain. Its superior and back surface is 

 a continuation of the lining membrane of the nose, and its anterior or inferior one, 

 that of the palate. It is called the velum palati, or veil of the palate. It extends as 

 far back as the larynx, and lies upon the dorsum of the epiglottis, and is a perfect 

 veil or curtain interposed between the cavities of the nose and mouth, cutting off all 

 communication between them. Tied by its attachment to the palatine bone, it will 

 open but a little way, and that only in one direction. It will permit a pellet of food 

 to pass into the oesophagus; but it will close when any pressure is made upon it from 

 behind. Two singular facts necessarily follow from this : the horse breathes through 

 the nostrils alone, and these are capacious and easily expansible to a degree seen in 

 no other animal, and fully commensurate to the wants of the animal. 



It is also evident that, in the act of vomiting, the contents of the stomach must be 

 returned through the nostril, and not through the mouth. On this account it is that 

 the horse can with great difficulty be excited to vomit. There is a structure at the 

 entrance of the stomach which, except under very peculiar circumstances, prevents 'its 

 return to the throat, and consequently to the mouth. 



The muscles of this singular curtain are ver}- intelligibly and correctly described by 

 Mr. Percivall, in his "Anatomy of the Horse," to which the reader is referred. The 

 same remark is applicable to a very singular and important bone, and its muscular 

 apparatus, the os hyoides. 



THE LARYNX 



Is placed on the top of the windpipe (see 1, p. 7"3), and is the inner guard of the 

 lungs, if any injurious substance should penetrate so far; it is the main protection 

 against the passage of food into the respiratory tubes, and it is at the same time the 

 instrument of voice. In this last character it loses much of its importance in the 

 quadruped, because in the dumb animal it is a beautiful piece of mechanism. 



The Epiglottis (see 2, p. 72) is a heart-shaped cartilage, placed at the extremity 

 of the opening into the windpipe, with its back opposed to the phar}'nx, 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, as already described, closes the aperture of the 

 larynx, and prevents any portion of the food from entering it. The food having 

 passed over the epiglottis, from its own elasticitj- and that of the membrane at its 

 base, and more particularly the power of the hyo-epiglotideus muscle, rises again and 

 resumes its former situation. 



The Thyroid Cartilage (see 1, p. 72) occupies almost the whole of the external 

 part of the larynx, both anteriorly and laterally. It envelopes and protects all the 

 rest; a point of considerable im])(>rtance, considering the injury to which the larynx 

 is exposed, by our system of curbing and tight reining. It also forms a point of 

 attachment for the insertion of the greater part of the delicate muscles by which the 

 other cartilages are moved. 



The beautiful mechanism of the larynx is governed or worked by a somewhat com- 

 plicated system of muscles, for a description of which the reader is referred to the 5th 

 vol. of The Veterinarian, p. 447. It is plentifully supplied with nerves from the res- 

 piratory system, and there are also frequent anastomoses with the motor nerves of the 

 spinal cord. The sole process of respiration is partly under the control of the will, 

 and the muscles of the larjmx concerned in one stage of it are likewise so, but they 

 also act independently of the will, for during sleep and unconsciousness the machine 

 continues to work. 



The origin of the artery which supplies these parts with blood is sometimes derived 

 from the main trunk of the carotid, but oftener it is a branch of the tliyroideal artery. 



