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infant I have found them in the last divisions of the bronchial tubes, 

 and their dilated extremities, but not in the penultimate or earlier 

 branches ; and even in the last divisions they are not always present 

 previous to the dilatation. In respect of the extent, therefore, to 

 which these alveoli exist in the human lung, my observations do not 

 quite accord with those of Rossignol. 



The Blood-vessels of the Lungs. The branches of the pulmonary 

 artery accompany the bronchial tubes, arrived at the extremity of 

 which, they give off branches to the bronchial alveoli, and terminate 

 in vessels which take their course in the walls of the air- sacs in no 

 very definite or regular manner. From these vessels the pulmonary 

 plexus arises. 



The pulmonary veins, receiving the blood from the plexus of the 

 air-sacs, pass from the periphery of the lobulettes, and running in 

 the spaces between the lobules, make their way, independently, to 

 the root of the lung. 



The pulmonary plexus is situated in the walls which separate the 

 air-sacs, in the septa of the alveoli, and around the margins of the 

 openings which exist in the sacs. The plexus consists of a single 

 layer of vessels, which, as already pointed out by Mr. Rainey, is in 

 no instance doubled on itself. In the septa of the alveoli, and in the 

 margins of the orifices alluded to, the plexus does not reach quite to 

 the free border of the membrane composing them. 



There is no distinct and separate vessel for each alveolus, but the 

 branches of the terminal artery take their course along the walls of 

 the air-sacs, and give on 7 branches which for the most part run in 

 the septa of the alveoli ; some of them, however, pass across the 

 alveoli. From these vessels, and from the branches first mentioned, 

 the capillary plexus arises. The plexus, when formed, maintains a 

 tolerably uniform size throughout. In a well-injected preparation, 

 inflated and dried, it will be seen that the spaces between the vessels 

 are somewhat greater in diameter than the vessels themselves. 



The branches of the pulmonary artery do not anastomose till they 

 reach the termination of the bronchial tubes ; on the air-sacs they 

 anastomose freely. It is somewhat difficult to decide whether the 

 vessels of one lobulette anastomose with those of another. On look- 

 ing at a preparation injected and dried, it seems as though the 

 septum, separating one lobulette from another, resembled in every 



