. The American journal of anatomy . much the exact point occupied in agiven type by a given bronchus, but how did it attain that lo-cation in the course of phyletic or ontogenetic us examine some of the details of the problem more closely. At the outset it will become apparent that the theory, if car-ried back to its logical starting point, will bring us to a novel con- 138 GEO. S. HUNTINGTON cept of the early phylogenetic type of bronchial unfolding. Ifthe right eparterial and cardiac bronchi of the prevalent typewere primarily derivatives of the first ventral bronchus, the fo
. The American journal of anatomy . much the exact point occupied in agiven type by a given bronchus, but how did it attain that lo-cation in the course of phyletic or ontogenetic us examine some of the details of the problem more closely. At the outset it will become apparent that the theory, if car-ried back to its logical starting point, will bring us to a novel con- 138 GEO. S. HUNTINGTON cept of the early phylogenetic type of bronchial unfolding. Ifthe right eparterial and cardiac bronchi of the prevalent typewere primarily derivatives of the first ventral bronchus, the for-mer a dorsal, the latter a ventro-medial branch, and if in therest of the series all dorsal, dorso-medial, and ventro-medialcomponents of the stembronchus were originally derivatives fromthe primary ventro-lateral bronchus of their respective levels,then these premises would define the most primitive mammalianor promammalian stem-bronchus as giving origin solely to mon-opodic ventro-lateral derivatives, whose secondary branching. Fig. 4* Hypothetical plan of the primitive derivatives of the stem-bronchus,as stipulated by the Migration Theory. carries their distribution into the remaining dorsal, dorso-medialand ventro-medial districts. The schematic cross section of ahypothetical reconstruction of this bronchial type would appearas in figure 4^. Migration then becomes responsible for the re-distribution of the components shown in figure 4®. The pulmonary organization represented in figure 4^ is notfound in the phyletic series. If this is accepted as indicating the earliest phylogenetic mam-malian type of bronchial organization, one of two conclusionswould be inevitable: a. Either the mammalian lung represents the persistence of amore primitive pulmonary type than that found in the embryoor adult of any of the extant lower vertebrates, or PULMONARY EVOLUTION IN MAMMALIA 139 b. The mammalian lung is a cenogenetic structure and doesnot represent the end-link in a continuous evo
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectanatomy, bookyear1920
