230 RESPIRATORY SYSTEM. 



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 por- 

 tions of the pleura : everywhere 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 in- 

 deed much resemblance : for, though the two lungs are not sym- 

 metrical, yet, both together, they put on this shape, which is 

 the counterpart of that of the cavity they occupy. With regard 

 to their general figure, however, the lungs may be said to be 

 conical : being broad and concave posteriorly, where they are 

 opposed to the convex surface of the diaphragm ; narrow and 

 somewhat pointed anteriorly, where they are received into the 

 blind pouches of the pleura, in the space between the two first ribs. 



Co/our. — In colour, these organs vary somewhat, depending 

 upon the age of the animal, and upon the quantity and distribu- 

 tion of the blood they contain. In the young subject, they are 

 of a lighter and more uniform shade than in the adult. In per- 

 fect health they assume a pink hue ; which, as age advances, 

 becomes mottled with purple and greyish patches. Sometimes, 

 in the dead subject, they are found of the colour of the darkest 

 venous blood, which arises from an inordinate congestion of 

 that fluid within the pulmonary veins. 



.Struct u}-e. — The lungs are composed of the branches of arteries 

 and veins, and of the ramifications of the trachea ; all which 

 vessels are connected together by an abundant, intervening cel- 

 lular substance, known by the name of parenchyma. Beneath 

 the curve made within the chest by the posterior aorta, the tra- 

 chea divides into the two bronchial tubes, of which the right, is 

 the larger, but the shorter : the left the longer, in consequence 

 of having to pass under the aorta in order to reach the left lung. 

 Having entered the substance of the lung, the right tube divides 

 into four others ; the left only into three ; which difference arises 

 from the right lung possessing an additional lobe : these branches 

 may be traced for a considerable extent within the parenchyma, 



* 1 consider, in comparison with the boily, that they exceed in luai^iii- 

 tiide those of the huuiuii subject. 



