RESPIRATION. 



275 



veins proceeding from several lobules unite 

 together into a trunk common to them all. 

 The larger trunks, resulting from the conflu- 

 ence of the smaller, converge towards the 

 roots of the lungs, but by a route different 

 from that of the bronchia and arteries. Thus 

 the general mass of the lung may be -regarded 

 as containing two series of ramified canals; 

 one transmitting the bronchial tubes, the nerves 

 and pulmonary artery, the other the pulmo- 

 nary veins. This interesting fact was well 

 described by Dr. Addison of Guv's Hospital 

 in a paper in the Medico Chirurgical Trans- 

 actions in 1840. At the root of the lungs 

 four pulmonary veins result, which discharge 

 their blood into the left auricle. " The cause of 

 the separate course of the pulmonary arteries 

 and veins is to be found in the opposite posi- 

 tion of their radicles in regard to the capillary 

 net-work of the lobules, it being a convenient 

 arrangement for the terminal arterial and 

 venous twigs to hold alternate positions 

 among the capillary net-work, so that each 

 arterial twig dispenses its blood in all direc- 

 tions, and each venous radicle collects it from 

 all sides." * 



The Bronchial System of Vessels consists of 

 arteries and veins. The bronchial arteries are 

 commonly described as the nutrient vessels 

 of the bronchial tubes. They arise from the 

 front of the descending or thoracic aorta. They 

 are, however, variable in number as well as in 

 place of origin. They are commonly described 

 as the inferior and superior. 



The superior, two usually in number, arise 

 either separately or by a common trunk from 

 the front of the aorta, opposite the third or 

 the fourth dorsal vertebra, and one directed 

 to each side adheres to the posterior surface 

 of the bronchial tube, on which it divides into 

 branches, and passes into the interior of the 

 lung. 



The inferior, two or more in number, arise 

 lower down than the preceding, and are distri- 

 buted, like them, on the bronchus of each 

 lung : these small arteries give branches to 

 the oesophagus, bronchial glands and pericar- 

 dium. The superior bronchial artery of the 

 left side may arise from the superior inter- 

 costal artery. Every successful injection ex- 

 hibits large and long branches from these ves- 

 sels, leaving the tracks of the bronchi, and 

 entering into the inter-lobular tissue and 

 sub-pleural tissue, -j- 



The bronchial Veins accompany the arteries, 



* Physiol. Anat. by Todd and Bowman, p. 393. 

 vol. ii. 



t In an excellent paper recently read before the 

 : Society (June ( Jth, 1853), Dr. Heale states this 

 till more strongly. He denies that the vascu- 

 lar plexus, distributed over the walls of the bron- 

 chial tubes, is derived at all from this system of 

 '-, but from the pulmonary rete. I have re- 

 peatedly remarked, that the Iron chial plexus cannot 

 be injected from the aorta. I ascribed the circum- 

 stance always to some imperfection in the attempt. 

 It will be seen in the text further on, however, that 

 my injections prove the presenceof a bronchial plexus 

 on the exterior of the bronchial tubes, though not 

 on the interior. 



and the branches unite one for each side ; 

 the right opens into the azygos vein, and the 

 left into the superior intercostal vein. Many 

 branches may be traced also to the oesopha- 

 geal veins, and those of the posterior medias- 

 tinum. Numerous branches of these veins 

 may be observed to wander under the pleura, 

 in the sub-pleural tissue. 



Anastomoses between the Bronchial and Pul- 

 monary Systems of Vessels. Since the days of 

 Ruysch, Haller, Soemmering, and Reisseissen, 

 this has proved a vexed question in anatomy. 

 One point in this controversy has been over- 

 looked. The bronchial arteries are said to be 

 the nutrient vessels, not of the lungs, but of 

 the bronchi. The tissue composing the struc- 

 ture of the air-cells and intercellular passages 

 of the lungs is nourished by the blood of the 

 pulmonary system. In the lungs of Reptiles 

 there exists no bronchial system of vessels. 

 The solid walls of these organs are occupied 

 exclusively by the pulmonary system. It is 

 upon the latter, therefore, that the function of 

 nourishing the substance, the parenchyma, of 

 these organs must devolve in these animals. 

 Thus is proved the capacity of this blood. 

 The epithelial particles and elastic fibres; of 

 the air-cells derive the materials of their nu- 

 trition from the blood of the plexus (the true 

 pulmonary) on which they immediately lie. 

 It is indisputable, therefore, that the afferent 

 blood of the lungs, like that of every other 

 gland, discharges a twofold office, that pro- 

 per to the gland, and that of nourishing its 

 tissue. Two systems or layers of capillary 

 plexuses are discoverable on the walls of the 

 bronchial tubes ; one lies immediately under- 

 neath the mucous membrane, and exhibits ex- 

 tended oblong meshes, which run parallel with 

 the yellow elastic fibres; the other lies on 

 the outside of the circular muscular layer, so 

 that the stratum of muscles is interposed be- 

 tween the two systems of vessels. This outer 

 layer of vessels, its trunks and capillaries, run 

 circularly with the fibres of the muscles and 

 at right angles with those of the submucous 

 layer. The blood of the former empties itself 

 into the pulmonary vessels ; that of the latter 

 (the outer) returns by means of the bronchial 

 veins. This, in brief, is the result of the au- 

 thor's investigations. They are confirmatory 

 of those of Adriani. The mode in which the 

 bronchial and pulmonary vessels communicate 

 is stated differently by different authors. Some 

 suppose that the blood of the bronchial arte- 

 ries is poured directly into the pulmonary 

 artery, with the venous blood of which it 

 admixes, and like which, traversing the respi- 

 ratory plexus, becomes arterialised before it 

 reaches the left auricle. On this supposition 

 the blood entering the left auricle would be 

 purely and exclusively arterial. By other ana- 

 tomists of these Rossignol is the most pro- 

 minent* it is contended that the bronchia 



* " Dans les injections faites paries arteres bron- 

 chiques, le liquide revenait en abondance par les 

 veines pulmonaires, en bien moindre quantite par 

 tubes, though not les veines bronchiques, et on n'en retrouvait aucune 

 trace dans les rameaux de Partere pulmonaire,** 



T 2 



