174 Journal of the ^Mitchell Society [3Iar('h 



the pulmonary arteries from the right ventricle and the bronchial 

 arteries from the aorta. Typically" the pulmonary veins drain the 

 lungs of the blood brought in by the pulmonary arteries and, through 

 connecting capillaries, a small amount of the blood brought in by the 

 bronchial arteries reaches the pulmonary veins. Most of the blood 

 brought in by the bronchial arteries, however, is carried away from 

 the capillary plexuses around the ])ronehi l)y small bronchial veins 

 which empt.y into the azygos and accessory hemi-azygos veins, repre- 

 sentatives of persisting portions of the embryonic cardinals. Condi- 

 tions similar to that shown in the anomaly that I have cited appar- 

 ently arise as a result of some interference with the return of the 

 blood through the pulmonary portion of the embryonic splanchnic 

 plexus, thus causing both pulmonary and bronchial blood to enter the 

 bronchial veins and resulting according to the laws of Thoma (3) 

 in the enlargement of the bronchial system and an atrophy and dis- 

 appearance of that part of the splanchnic plexus which would have 

 formed the left pulmonary vein. 



Laws of Thoma (4) : 



(1) An acceleration of the current leads to an enlargement of the lumen of a 

 vessel, and a slowing of the current leads to its narrowing and final 

 disappearance. 



(2) An increase in the blood pressure is the cause for new formation of 

 capillaries. 



(3) The growth in thickness of the vessel wall depends on the tension of the 

 wall, which in turn is dependent upon the blood pressure and the diameter 

 of the vessel. 



In this particular case then the large vein passing from the upper 

 left lobe of the lung to the left innominate vein would be composed 

 of the left bronchial vein and that portion of the accessory hemi- 

 azygos between the innominate and the junction of the bronchial with 

 the accessory hemi-azygos. On account of the great enlargement of 

 this vein the distal portion of the accessory hemi-azygos appears as 

 a side branch of the "anomalous pulmonary." 



Chapel Hill, N. C. 



LITEEATURE CITED 



(1) Bailey and Miller: Text-book of Embryology, p. 258, 4th ed., 1921. 



(2) Alfred Brown: The Development of the Pulmonary Veins in the Domes- 

 tic Cat. Anat. Record 7:299. 1913. 



(3) R. Thoma: rntersuchungen ueher die Histogenese und Histomechanik 



des Gefiiss-systems. 8. 1-91. Stuttgart, 1893. 



(4) Quoted from Keibel and Mall's Textbook of Embryology 2:421. 112. 



