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by the limited environment of the bronchi, it becomes unequal, one 

 fork growing on so rapidly to become the stem, that the other is left 

 either as a small bud or a small side branch, which develops further 

 when the space relations permit. Later still when the total volume 

 of the lung is such that each bronchus is more or less equally sur- 

 rounded by mesoderm, the dichotomy is equal, although of the two 

 forks resulting from a division, one becomes the stem and the other 

 is shunted off as a side branch. The point, however, where monopody 

 ceases and dichotomy begins is apparently different in different species. 

 In the pig it is below Lateral 6 while in man according to His, the 

 transfer is made at Lateral 4. It must be remembered in this con- 

 nection, however, that the space relations in this region of the human 

 lung are quite different from those in the pig owing to the different 

 position of the heart, diaphragm and liver. 



The bronchi, apparently, show great adaptability both in the power 

 and direction of their growth. This interesting characteristic is best 

 shown when one of the chief bronchi are suppressed. Adjacent branches, 

 while still rooted firmly at their point of origin, then grow into the 

 area of the lung usually supplied by the suppressed element, a process 

 which, taken in connection with the extreme variation of the point of 

 origin of the bronchi, gives rise, in the adult tree, to the series of 

 pictures which suggest a wandering of the branches. In my whole 

 series of specimens numbering ten reconstructions and many cleared 

 specimens 3 to 18,5 mm, and about 100 corrosions of pigs from 4 cm 

 to the half grown stage, I have never found any evidence which pointed 

 to a wandering of any elements of the tree. The bronchi remain 

 attached to their stems where they are formed, although their branch- 

 ing is controlled to a great extent by the space in which they have 

 to grow. When this is altered by the suppression of one of the usual 

 elements, adjacent branches show a power of substitution which is 

 perhaps best exemplified in the fate of the two dorsal forks of the 

 first division of the right and left Lateral 2. On the right side, this 

 branch, owing to the presence of the Lateral 1 above it, is forced to 

 grow downwards and posterior to form a dorso-inferior branch of 

 Lateral 2, while on the left side, this same fork unobstructed by the 

 suppression of Lateral 1, grows up to substitute for the suppression 

 of left Lateral 1. 



Few of the many characteristics of the bronchial tree have given 

 rise to more discussion than the method of its growth. Between the 

 two extremes of dichotomy, most of the possible intermediate pro- 

 cesses have been described. A careful review of the literature on 



