152 



ANATOMY AND PHYSIOLOGY OF 



the cavity they occupy. With regard to 

 their general figure, however, the lungs may 

 be said to be conical : being broad and con- 

 cave posteriorly, where they arc opposed to 

 the convex surface of the diaphragm ; nar- 

 row and somewhat pointed anteriorly, where 

 they are received into the blind pouches of 

 the pleura, in the space betvveen the two 

 first ribs. 



Color. — In color, these organs vary some- 

 what, depending upon the age of the ani- 

 mal, and upon the quantity and distribution 

 of the blood they contain. In thfe young 

 subject, they are of a lighter and more uni- 

 form shade than in the adult. In perfect 

 health they assume a pink hue ; which, as 

 age advances, becomes mottled with purple 

 and grayish patches. Sometimes, in the 

 dead subject, they are found of the color of 

 the darkest venous blood, which arises from 

 an inordinate congestion of that fluid within 

 the pulmonary veins. 



Structure. — 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 abun- 

 dant intervening cellular substance, known 

 by the name of parenchyma. Beneath the 

 curv'e made within the chest by the poste- 

 rior aorta, the trachea 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 consid- 

 erable extent within the parenchyma, giv- 

 ing off in their passage numerous other 

 smaller tubes of similar structure ; but, as 

 we prosecute our dissection of them, we 

 shaU find that, in growing smaller, they par- 

 take less and less of the nature of cartilage, 

 and that the extreme ramifications are not 

 only entirely membranous in their composi- 

 tion, but of so fine a texture as to be per- 

 fectly transparent. It will be remembered 

 here, that, in speaking of the trachea, a 



membranous lining to it was described of 

 the mucous kind, which, it was observed, 

 thence passed into the bronchial vessels : 

 now, it is of the continuation of this mem- 

 brane in an attenuated state that the minute 

 air-tuoes appear entirely to consist ; at the 

 extremity of every one of which the mem- 

 brane is prolonged into a kind of blind bag, 

 or cul-de-sac, to which the name of air-cell 

 has been given. 



From the arborescent ramification and 

 peculiar mode of termination of the bron- 

 chical tubes, some anatomists have com- 

 pared them, and the cells at their extremities, 

 to a bunch of grapes — supposing the stalks 

 to represent the ramifications of the former, 

 and the grapes connected with them the 

 air-cells; others have described them as 

 having resemblance to a honeycomb : and 

 so far as the knife, with the aid of glasses, 

 can develope their intimate structure, the 

 first is an apt comparison, insomuch as it 

 relates to the disposition of their cells ; 

 the last, insomuch as it conveys an 

 idea of their ready inter-communication. 

 For, though they do not communicate 

 but through the ramifications of the bron- 

 chial tubes, this is a medium of inter- 

 course at once so general and free, that 

 numbers of them are inflated at the same 

 time by impelling air into any one of the 

 larger branches. With the parenchymatous 

 substance, however, they have no commu- 

 nication whatever.* 



The blood-vessels that enter into the com- 

 position of the lungs are denominated the 

 pulmonary. The pulmonary artery, having 

 taken its origin from the right ventricle of the 

 heart, winds upward to the root of the left 

 lung, and there divides into the right and 

 left pulmonary arteries, which divisions 



* If the substance of the hmgs be lacerated or rent 

 asunder, the surface ■will be found to present a tabulated 

 aspect. Introduce a blow-pipe into one of these lobuli, 

 and all the other lobules — the entire lung — may be in- 

 flated from this one ; showing the free communication ex- 

 isting between them. The same may be effected by in- 

 jecting quicksilver. You may do the same with the inter- 

 stitial substance ; but in this case you do not fill the lobules. 

 In fine, the lungs with their cells resemble a sponge ; only 

 that the connecting tissue has no communication with the 

 sponge. 



