CHAPTER VIL 



THE CONTENTS OF THE CHEST. 



THE THYMUS GLAND. 



At the entrance of the trachea into the thorax, and situated 

 in the doubhng of the anterior mediastinum, is an irregular 

 glandular body, called the thymus gland, or " sweet-breac." It 

 conveys a peculiar albuminous fluid to the vems, but its use in 

 the system is unlaiown. 



THE DIAPHRAGM. 



The interposed curtain extending across the cavity of the chest, 

 between the thorax and abdomen, is called the diaphragm (mid- 

 riff). It is an irregular muscular expansion, proceeding from the 

 inferior surface of the lumbar vertebrae posteriorly and superiorly, 

 adhering to the ribs on either side, and extending obliquely for- 

 ward and downward to the sternum ; or, rather it is a flattened 

 muscle arising from all these points, with its fibres all converging 

 towards the centre, and terminating there in an expansion of 

 tendinous substance. It is lined anteriorly by the pleura or in- 

 vesting membrane of the thoracic cavity, and posteriorly by the 

 peritoneum or investing membrane of the abdominal cavity. 



The diaphragm is the main agent, both in ordinary and extra- 

 ordinary respiration ; it assists also in the expulsion of the urine, 

 and it is a most powerful auxiliary in the act of parturition. 



It is subject to injury and disease of a serious and varied char- 

 acter. Whatever may be the original seat of thoracic or abdom- 

 inal ailment, the diaphragm soon becomes irritable and inflamed. 

 This accounts for the breathing of the horse being so much af- 

 fected under every inflammation or excitement of the chest or 

 belly. The irritability of this muscle is often evinced by a sin 

 gular spasmodic action of a portion, or the whole of it. 



Opium should be administered in small doses, together with 

 ammonia or nitric ether, and as soon as any reaction is observed 

 have recourse to bleeding. 



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