DEPARTMENT OF EMBRYOLOGY. 113 



The work of Dr. Robert S. Cunningham on the development of the 

 lymphatics of the lung is now concluded and forms Contribution No. 12 

 in Publication No. 224. Dr. Cunningham concludes that the develop- 

 ment of the lymphatics within the lung depends upon the division of 

 the vessels into two groups — those associated with the veins and con- 

 nective-tissue septa, and those associated with the arteries and the 

 bronchi. The former grow very rapidly, and, following each of the 

 branches of the pulmonary vein, pass to the pleura. There are at 

 first only two or three lymphatics with each vein. In the early stages 

 the terminal veins lie about midway between the adjacent bronchi, 

 and in this plane a sheet of lymphatics develops from the vessels 

 surrounding the veins and passes to the pleura, where they mark out 

 the boundaries of the distribution of each bronchus. These vessels 

 anastomose with those that grow direct to the pleura from the plexus 

 on the trachea. The bronchial vessels develop more slowly, and at 

 first are to be found only around the larger bronchi. As these struc- 

 tures increase in size and number, the lymphatics surrounding the main 

 bronchi send vessels to the smaller ones, and these form a plexus around 

 each of the bronchi, so that the bronchial tree is surrounded by a 

 continuous series of branching tubes made up of lymphatic vessels. 

 From every point of division of the bronchi, lymphatic vessels pass to 

 those of the veins. Those around the terminal bronchus leave it near 

 its ending in the atria, and pass to join the lymphatics of the veins or 

 septa, or, more rarely, those of the pleura. 



Lymphatics also arise from the retroperitoneal sac and grow upward 

 behind the diaphragm to enter the lower pole of the lower lobe of the 

 lung. These vessels form a plexus on the median surface of the lower 

 lobe, and send branches to the pleura of the other surfaces and into the 

 lung along the veins. Plexuses develop here, as is the case with those 

 that come from above, and the two groups soon anastomose. In the 

 adult there are lymphatic vessels accompanying the bronchi, the 

 arteries, and the veins; these anastomose freely. There are also vessels 

 in the connective-tissue septa which drain chiefly into those around the 

 veins, and, to some extent, into those of the bronchi and arteries, near 

 the point where the vein and the bronchus separate to take their rela- 

 tive positions in relation to the lobule. There are numerous anasto- 

 moses between the deep vessels and those of the pleura, but probably 

 most of the flow is toward the hilum. All the deep vessels, together 

 with the greater number of the pleural vessels, drain into the nodes at 

 the hilum; but the vessels of the lower half of the pleura of the lower lobe 

 drain through several vessels to the preaortic nodes. These vessels 

 pass through the ligament of the lower lobe and behind the diaphragm. 



The work of Mrs. Eleanor Linton Clark, which was alluded to in 

 previous reports, is now nearing completion. Her last publication 

 is upon the lymph-flow in the early superficial lymphatics in the living 



