98 EDWARD MCCRADY, JR. 



As in all other mammals, the pulmonary arteries arise (see 

 stage 30 in the opossum) as outgrowths of the sixth aortic 

 arches, or if you interpret it that way, as posterior extensions 

 of the ventral aortae at any rate, as branchial arteries. 

 The nerves to the lungs, the vagi, are universally considered 

 to represent a fusion of the posterior branchial nerves. All 

 of these facts have led me to believe that the lungs are 

 modified gill pouches. 



According to Goodrich ('30) this theory dates back to 

 Goette (1875). After a considerable period of neglect it has 

 been revived and championed by Makuschok ( '11, '12, '13) 

 and others. Evidence (not always recognized as such) has 

 accumulated from Amphibia, Reptilia, Aves, and Mammalia, 

 i.e., all the pulmonate groups ; but two objections have been 

 urged. First and most important is Greil's opinion that the 

 lung rudiments, though often paired and lateral in all these 

 groups, are in all cases that he knows too ventral to be homolo- 

 gous with gill pouches. That objection seems best answered 

 by the evidence from the opossum just presented, in which 

 the lungs at the beginning are definitely dorso-lateral, not 

 ventro-lateral, and are part of a conspicuous branchial ridge. 

 The second objection is simply that the lung pouches never 

 make contact with the ectoderm. This latter does not seem to 

 be an important criterion for there are other cases in which 

 gill pouches fail to make contact with the ectoderm, particu- 

 larly the more posterior ones for instance, the sixth in 

 Triton (Makuschok, '11) and the fourth and fifth in the rat 

 (Pischinger, '32). 



Having seen, therefore, that the lungs themselves arise 

 in the same manner and from the same source as the gill 

 pouches, that their blood supply and nerve supply are 

 branchial, that the cartilages of the trachea and bronchi as 

 well as those of the larynx are of branchial origin, and that 

 in the face of all this confirmatory evidence no important 

 contradictory evidence has been found, there seems to be no 

 escape from the conclusion that the lungs are modified gill 

 pouches. Makuschok has shown the same to be true of the 



