178 MILLER. [Vol. VIII. 



than those to the air-sacs, and those to the air-cells of the 

 terminal bronchus are smaller than those to the atria. None 

 of the arteries seem to pass directly to the surface of the 

 pleura, and it is very seldom that an artery passes to the per- 

 iphery of the lobule. A cast of the terminal artery with all 

 of its branches is given in Fig. 14. It was made by inject- 

 ing with celloidin and then digesting the tissues in artificial 

 gastric juice. The lobular artery, Z, breaks up into the atrial 

 arteries. A, which in turn give rise to the branches of the air- 

 sac, A. S. 



On reaching the air-sac the artery breaks up into small 

 radicals which pass to the central side of the sac in the sulci 

 between the air-cells, and are finally lost in the rich system of 

 capillaries to which they give rise (Fig. 16). This net-work 

 surrounds the whole air-sac and communicates very freely with 

 that of the surrounding sacs. When two sacs adjoin each 

 other a common net-work supplies both. In fact this is the 

 rule throughout the lung. Not only are the air-sacs covered 

 with this rich net-work of capillaries, but they also cover the 

 atria and also those air-cells which arise directly from the 

 terminal bronchus. The diameter of the capillaries is about 

 7/A, being slightly larger just beneath the pleura, and somewhat 

 smaller deeper in the lung. In length they are slightly larger 

 than their diameter, and the meshes of the net-work exceed, to 

 a slight extent, the diameter of the vessels. After the net- 

 work has extended over the whole air-sac or atrium to the 

 peripheral side of the air-sac they begin to form larger vessels 

 which are the beginnings of the veins. 



The vein radicels collect the blood from the air-sacs rather 

 than from the air-cells. They do, however, lie upon the cells 

 ©f a sac rather than in the sulci between them. These radi- 

 cels soon flow together, as shown in Fig. 16, and unite to form 

 the air-sac vein. The veins lying on the peripheral side of the 

 air-sac naturally lie between the lobules, and of course collect 

 blood from the sacs of three distinct lobules. Were it not for 

 the fact that the artery and bronchus lie in the center of the 

 lobule and that there is more connective tissue between the 

 lobules, it would be as easy to consider the vein in the center 



