274 



represented by a slight medial swelling of the end bud on the inner 

 side representing Medial 5, placed in this specimen almost opposite 

 Lateral 5. This series is quite irregular but in the pig's lung never, 

 in my experience, occurs higher than a short distance above Lateral 4 

 on either side. 



From this point, it is no longer necessary to describe the suc- 

 cessive appearance of the buds; the ditferent groups are produced in 

 the same way, that is to say, by monopody. Of the Laterals we have 

 usually six on the right side and five on the left, owing to the un- 

 paired lateral element on the trachea. They become paired at the 

 level of Lateral 2; left Lateral 1, like left Ventral 2 is always sup- 

 pressed in the pig's lung. It is not an uncommon occurrence, hewever, 

 to find one of the remaining lateral elements suppressed, or else, to 

 see an extra element formed giving extremes of variation for the 

 lateral series in the pig's lung between seven and five for the right 

 side, and six and four for the left, with an average of six right and 

 five left lateral bronchi. The ventral bronchi are formed below Lateral 2. 

 One, Ventral 2, on the left side, is always suppressed. The buds 

 for this series vary much in their position, although they are usually 

 placed near the middle of the interspace between the adjacent lateral 

 branches. At times they may be either near the higher or lower 

 lateral element, while again they may be absent, or still more rarely, 

 reduplicated. That is to say, two buds may form between adjacent 

 lateral bronchi, each of which will give rise to a ventral bronchus. 

 I possess several specimens where this has occurred, although the 

 remainder of the series, with the exception of left Ventral 2, is ab- 

 solutely complete. 



The dorsal series, developing in a similar way, show the same 

 characteristics. With a great variability in the site of their origin, 

 the frequent suppression of an element occurs and less frequently, a 

 reduplication. Thus we may have, as on the ventral side, either mis- 

 sing elements or a complete dorsal series on each side with an extra 

 branch placed between two lateral bronchi. 



The median series are extremely irregular in their arrangement. 

 They, like the laterals, form chiefly from the sides of the end buds, 

 but never in my experience do they occur higher than a short distance 

 above Lateral 4. They, too, vary even in wider limits and may be 

 placed at the level of the corresponding lateral bronchi or at any 

 point between them. They may not be present at all, they may be 

 doubled, or may occur only on one side. In consequence of this 

 extreme variability of the various elements derived from the stem 



