Joseph Marshall Flint 85 
is absent on one side or both; C represents lungs where a Lobus infra- 
eardiacus is present, and by eliminating this lobe and altering the topo- 
graphy of the ventral bronchi, it may be used for lungs where V. 2 is 
either absent or included in the Lobus inferior. For example, B repre- 
sents the conditions found in Hystrix cristata in both lungs where not 
only all of the primary bronchi in that animal have produced lobes, but 
some of them are still further partially subdivided. There is also a 
type of lung represented by Phoca vitulina where L. 1 is present on both 
sides, but L. 2 in this species is thrown into the Lobus inferior. For this 
state of affairs 4 would suffice if the permanent fissure between L. 2 
and L. 3 were replaced by a dotted line. The suppression of the lobes 
indicated in Phoca vitulima may involve all fissures giving us a lobeless 
lung like those of Delphinus delphys and Pithecus satyrus. 
It is, of course, clear from the above description how we regard the 
equivalent values of the lobes on the two sides, but they may be simply 
stated in two simple formule of equivalence which will fit the lungs of 
most animals depending upon the presence of L. 1 and V. 2 on one or 
beth sides. Type 1 includes the great majority of mammalian lungs. 
Type 1. Type 2. 
L.1 present only on the right side. L. 1 present or absent on both sides. 
Right Side. Left Side. Right Side. Left Side. 
Lobus superior — O. Lobus superior — Lobus superior. 
Lobus medius = Lobus superior. Lobus medius = Lobus medius. 
Lobus inferior = Lobus inferior. Lobus inferior = Lobus inferior. 
or or 
Lobus inferior + V.2—=Lobus in- Lobus superior — Lobus superior. 
ferior + V.2 or O. Lobus inferior — Lobus inferior. 
While lobe production in the lungs is obviously dependent on the 
growth of the bronchi in the. majority of instances, the number of lobes 
is apparently without definite morphological significance. It may vary 
in animals from multilobed lungs like those of Hystrix to lobeless lungs 
like those of Pithecus satyrus. The common relationships, however, are 
expressed in the types given above. 
THE ORGANOGENESIS OF THE LUNGS. 
In turning to the organogenesis of the lungs from the period of the 
formation of the Anlage until the adult stage is reached, the first interest 
settles in the chief cells of the bronchi and the pulmonary connective 
tissue. Both of these structures have been followed up to the age repre- 
sented by a pig 10 mm. long, in the chapter on the development of the 
