THE DIAPHRAGM. 197 



CHAPTER XI. 

 THE BELLY AND ITS CONTENTS. 



THE DIAPHRAGM. 



The chest is separated from the abdomen or belly, by the diaphragm 01 

 midriff, which extends obliquely from the loins to the breast-bone. In its 

 natural state it is convex, or projecting forward towards the lungs, and 

 concave or hollow backward towards the stomach and intestines. On the 

 side towards the chest it is covered by the membrane which invests the 

 lungs, and towards the belly by that which covers the intestines. It is 

 attached to the spine, the ribs, and the breast-bone, by tendinous or fleshy 

 expansions, and in the centre it is composed of strong muscular fibres : it 

 is one of the most important muscles of the frame ; and is, as we have de- 

 scribed it, the principal agent in breathing. When it acts, its fibres are 

 shortened ; it loses its convexity, and becomes plane ; the chest is thereby 

 enlarged, and the lungs enlarge with the expansion of the cavity in which 

 they are placed ; and air rushes in, and inspiration is performed. When 

 the fibres of the diaphragm cease to act, that muscle returns to its natural 

 form ; it becomes again convex ; it presses upon the lungs, and helps to 

 force out the air, and expiration is accomplished. It assists likewise in the 

 natural constant motion of the bowels, and lends its powerful aid in the 

 expulsion of the dung and urine, and in the birth of the young animal: it is 

 most concerned in coughing, yawning, sighing, &c. The membrane which 

 covers the diaphragm is very subject to inflammation. Whether the ori- 

 ginal seat of disease be in the lungs or the bowels, the diaphragm soon 

 becomes inflamed and irritable, which accounts for the breathing of the 

 horse being so much affected under every inflammation of the chest or belly. 

 The. diaphragm is likewise occasionally ruptured, principally from violent 

 exertion. It has so much to do in the act of breathing, that it is not to be 

 wondered if, when the respiration is exceedingly hurried, this muscle should 

 give way. The symptoms of ruptured diaphragm are very obscure: there 

 are none on which we can perfectly depend. This, however, is a matter 

 of little consequence, for it is uniformly fatal. If the rupture be small, 

 some portion of the intestine insinuates itself, and becomes entangled, and 

 the passage is incurably obstructed ; and if the aperture be large, so much 

 of the intestine passes through as to press upon the lungs, and render 

 breathing impossible. 



Three large vessels pass through the diaphragm : the great artery which 

 conveys the blood from the heart to the hinder part of the frame, and which 

 goes through a kind of division of the diaphragm, so that it cannot be 

 pressed upon ; the great vein carrying the blood from the hinder parts and 

 the liver to the heart, and which penetrates the firm tendinous part of the 

 diaphragm so as likewise to be preserved from pressure; and the gullet, 

 which passes through the most fleshy portion of the diaphragm, and is liable 

 to be compressed by the constant action of this muscle, which, however, is 

 a matter of little consequence, for there is sufficient power in the muscles 

 of the gullet to propel the food through the diaphragm into the stomach. 



