140 On the Origin of the Pulmonary Arteries in Mammals 



at first almost horizontally across to the right side of the trachea, then 

 bending down toward the right lung, the left pursuing a straight course 

 to the left lung. The portion of the left fifth arch posterior to the 

 pulmonary arteries becomes later the Ductus Botalli, and is closed at 

 birth. 



It will be seen from this description that, in the actual origin of the 

 pulmonary arteries, the rabbit is identical with birds and reptiles, as 

 drawn by Rathke and verified by many other writers. In the rabbit, as 

 well as in birds and reptiles, one pulmonary artery arises from each 

 pulmonary arch, but in birds and reptiles the growth of these arches 

 is equal until birth, so that the picture is symmetrical, a fifth arch, a 

 pulmonary artery, and a Ductus Botalli on each side; while in the 

 rabbit the left pulmonary arch alone remains until birth, and the pic- 

 ture is distorted. It was this distortion, this early disappearance of 

 that portion of the right pulmonary arch posterior to the pulmonary 

 artery, which made possible the diagram of Eathke, and his statement 

 that '^in mammals the left fifth aortic arch at a very early period of 

 embryonic life sends out from about its mid-point a small branch which 

 is intended for both lungs, and posterior to its place of origin divides 

 into two twigs." 



Eathke examined, of mammals, the pig, sheep, and hare, with special 

 reference to the pulmonary arteries.^ In the rabbit, cat, and in the 

 few human embryos within my reach, I have found the pulmonary 

 arteries to arise as I have stated, that is, in the beginning, symmetrically, 

 one from each pulmonary arch. In Eathke's original diagrams the 

 arteries of lizards and of birds arise symmetrically, as do they also in the 

 frog, as described by Gaupp.^ Of snakes, according to Stannius and 

 others, while most species have only the right lung, and therefore only 

 the right pulmonary artery, in adult life, some species have the left 

 lung and left artery alone, and others even both lungs and both arteries, 

 more or less fully developed. In two cases, recently cited by F. Hoch- 

 stetter,^ of Trojudonotus tessellatus (a species with only the right lung 

 normally developed), a slender artery was found, which, although finally 

 ramifying in the oesophageal wall, resembled in origin and course a left 

 pulmonary artery. From these facts it seems probable that in the 

 younger snake embryos, of all species, both pulmonary arteries will be 

 found present. If this is the case, the proof will be strong that in all 



iMiiller's Archiv, 1848, p. 276. 



2 Anatomic des Frosches, diagram, p. 285. 



3 Morpliologisches Jahrbucb, 1901, p. 419. 



