"tPE HORSE. 



151 



acutely painful in the human subject than 

 pleurisy, and we have every reason to be- 

 heve that horses suffer much from the same 

 malady. 



Secretion. — It has been observed that 

 the exhalents of the pleura secrete a serous 

 fluid, which is emitted, in the form of an 

 exhalation or vapor, into the cavity of the 

 thorax ; and that it may be rendered visible 

 at any time, if an animal, recently dead, 

 be opened while yet warm ; or if an open- 

 ing be made into the chest of a live animal. 

 In either case, a whitish steam will be per- 

 ceived to issue from the interior of the 

 cavity. This vapor, shortly after death, be- 

 comes condensed and converted into a 

 liquid ; which accounts for the contiguous 

 surfaces of the pleura being moist, and for 

 a collection of more or less fluid, resem- 

 bling water, existing in the most depending 

 parts of the cavity. In consequence of 

 every part of the membrane being bedewed 

 in this manner, the lung itself may be said 

 to be in an insulated state ; for the pleura 

 costalis does not, philosophically speaking, 

 touch the pleura pulmonalis, nor is the lat- 

 ter in actual contact with the mediastinum : 

 all friction, therefore, in the motions of these 

 parts, is by this interfluent secretion effec- 

 tually prevented. In this, then, consists 

 the chief use of the pleura, viz., to furnish 

 a secretion for the purposes of lubrication 

 and facility of motion, which it further 

 promotes by its extreme glibness of surface. 

 It is said also to answer the purpose of 

 ligaments to the contained organs, thereby 

 confining and strengthening them. The use 

 of the mediastinum is to divide the chest 

 into two compartments. 



LUNGS. 



The lungs (by butchers called the lights) 

 are two. spongy bodies formed for the pur- 

 pose of respiration. 



Situation and Relation. — They are con- 

 tained in the lateral regions or sides of the 

 thoracic cavity ; separated from each other 

 by the mediastinum and heart, which occupy 

 the middle region. Prior to any opening 

 being made into the thorax, the lungs con- 



tinue to fill up every vacuity : no sooner, 

 however, is a perforation made into the 

 thoracic cavity than they shrink in volume, 

 and become in appearance too small for the 

 spaces they occupy. This arises from their 

 being during life — or rather during the 

 unopened state of the thorax — in a con- 

 stant state of inflation with atmospheric 

 air, which preserves them expanded ; and 

 they suffer collapse of substance the instant 

 air is admitted, in consequence of the pres- 

 sure of the atmosphere upon them, from 

 which they were protected before by the 

 parietes of the thorax. 



Division. — The lungs are two in num- 

 ber, the right and the left liing ; parti- 

 tioned from each other by the mediasti- 

 num. A further division of these organs 

 has been made into lobes. That on the 

 right side, the larger of the two, consists of 

 three lobes ; the left, only of two. These 

 lobes, which are nothing more than partial 

 divisions of the lung by fissures of variable 

 extent through its substance, serve to adapt 

 them more accurately to the thoracic cavi- 

 ties, and, at the same time, render them 

 fitter for the purposes of expansion and 

 contraction. 



Volume. — The lungs of the horse, when 

 inflated, are of great bulk ; * and the right 

 is the larger of the two : in consequence of 

 the heart being inclined to the left side, less 

 space is given for the left lung. 



Attachment. — The lungs are attached, 

 superiorly, to the spine (which attachment 

 is sometimes called their roots) by blood- 

 vessels, the divisions of the trachea, and the 

 mediastinal portions of the pleura : every- 

 where else, in a healthy subject, they are 

 free and unconnected. 



Figure. — In form, the lungs of the horse 

 are very like those of the human subject ; 

 and the latter have been compared to the 

 foot of an ox, to which the injected lung of 

 the foetus bears indeed much resemblance ; 

 for, though the two lungs are not symmetri- 

 cal, yet, both together, they put on this 

 shape, which is the counterpart of that of 



* I consider, in comparison with the body, that they 

 exceed in magnitude those of the human subject. 



