254 AXATOMY AXD DISEASE OF THE RESPIRATORY ORGANS. 



CHAPTER XIII. 



THE ANATOMY AND DISEASES OF THE RESPIRATORY ORGANS. 



Having in tlie previous chapter given a brief outline of tlie external 

 torn.ation of the chest, and surrounding parts, we now proceed to a de- 

 scription of its contents, and the organs directly connected with the func- 

 tions of respii^ation. 



THE DIAPHRAGM. 

 Bounding the thorax posteriorly— the base of the cone in the human 

 subject— the interposed curtain between the thorax and the abdomen in 

 the horse, is the diaphragm. It is an ii-regular muscular expansion, pro- 

 ceeding from the inferior surface of the lumbar vertebra? posterioriy and 

 superiorly, adhermg to the ribs and cartilages on either side, and extendino- 

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

 muscle arising from all these points, with its fibres all convergino- towards 

 the centre, and termmatmg there in an expansion of tendinous substance, 

 it IS lined anterioriy by the pleura or investing membrane of the thoracic 

 cavity ,_ and posteriorly by the pei^itoneum or investing membrane of the 

 abdominal cavity. 



Anato7nij of the Blaplragm.—ln the short account which it is proposed 

 to give of the structure of the diaphragm, the description of Mr Per- 

 civall will be closely followed. ' The diaphragm may be divided into the 

 mam cu-cular muscle, with its central tendinous expansion formino- the 

 -lower part, and two ajjj;ert(iice.s, or crura, as they are called, from^their 

 peculiar shape, constituting its superior portion. The fleshy orio-in of the 

 grand muscle may be traced laterally and inferiorly, commencint^^from the 

 cartilage of the eighth rib anteriorly, and closely follov\dng the union of 

 the posterior ribs with their cartilages ; excepting, however, the two last 

 The attachment is peculiarly strong ; it digitates with the transverse muscle 

 of the abdomen, and encii-cles the whole of the lateral and inferior part of 

 the chest, as far as the sternum, where it is connected with the ensi- 

 form cartilgae. Immediately under the loins are the appendices of the 

 diaphragm, commencing on the right side, from the inferior surfaces of 

 the five lumbar vertebra?, by strong tendons, which soon become muscular 

 and form a kind of pillar ; and on the left, proceeding from the two first 

 lumbar vertebra only, and from the sides rather than the bodies of these 

 vertebrae, and these also unite and form a shorter pillar, or leo-. The left 

 crus, or appendix, is shorter than the right, that it may be more out of the 

 wayof pressure fromthe left curvature of thestomach,which,Aviththespleen 

 lies underneath. Opposite to the seventeenth dorsal vertebrce these two 

 pillars unite and form a thick mass of muscles, detached from the vertebra? 

 and leaving a kind of pouch between them and the vertebra?. They not only 

 unite, but they decussate; their fibres mingle and again separate from each 

 other, and then proceed onward to the central tendinous expansion towards 

 which the fibres from the cu^cular muscle, and the appendices, all convero-e ' 

 This muscle, so important in its oflace, is plentifully supplied with blood- 

 vessels. As the posterior aorta passes beneath the crura of the diaphrao-m, 

 it gives out sometimes a single vessel which soon bifiu-cates ; sometimes 

 two branches, which speedily plunge into the appendices or crura while 

 numerous small vessels, escaping from them, spread over the central tendi- 

 nous expansion. As the larger muscle of the diaphragm springs from the 

 sides and the base of the chest, it receives many ramifieationl from the 



