6 The Development of the Lungs 
branches appear. These are produced by buds or hernial projections from 
the wall of the bronchus. Upon the stem bronchus are produced, ac- 
cording to Hesser, a lateral and medial row of buds, a result in which he 
is not in accord with Moser, who believes that there are three series, a 
lateral, ventral, and dorsal. Especially noteworthy is the fact that in 
land turtles the lateral bronchi form dilated sacs which later grow into 
wide ducts, while in the sea turtles the buds grow out as small tubes 
somewhat dilated at the ends. 
The question of the unequal development of the snake’s lung has re- 
cently been taken up again by Schmalhausen, 05, who finds in Tropi- 
donotus natrix an unpaired pulmonary anlage. From its caudal end, 
appears later the two projections for the lungs, which grow unequally 
but continuously throughout embryonic life. The enormous overgrowth 
of the right lung leaves the left as a slight appendix upon it. There is, 
apparently, no regressive change such as Rathke supposes takes place 
in Coluber natrix. Schmalhausen’s observations support Baumann’s 
supposition on this point. More important, however, is a still further 
confirmation of the work of Moser and Hesser as the lung of Tripido- 
notus natrix grows not through the development of axipetal septa pro- 
duction but from an outward budding of the lung wall. 
In view of these researches of Moser, Hesser, and Schmalhausen, then 
we may look upon respiratory apparatus of vertebrates as the resultant 
of a common principle of growth, and, in turning to the consideration 
of the ontogeny of the mammalian lung, there is good ground for believ- 
ing that its developmental processes no longer conflict with its phylo- 
geny. The evolution of the pulmonary system of mammals was first 
studied by Kolliker, 79, who traced the development of the organ in 
rabbits. It appears from an unpaired anlage which arises behind the 
gill pouches. This is produced by longitudinal furrows which separate 
the head gut into a dorsal and ventral portion from the latter of which 
the lungs arise, while the former forms the cesophagus. On the tenth 
day, the lower part widens so that the lung anlage forms a half canal 
which ends caudalwards in two round depressions. Through a longi- 
tudinal fissure, the anlage is still in communication with the cesophagus, 
while both structures are surrounded by a mass of mesoderm. The 
projections forming the rudiments of the lungs grow rapidly and bend 
dorsalwards, and, at the same time, the trachea and cesophagus begin 
to separate. This process starts at the posterior end of the juncture and 
progresses towards the head. 
A few years later Uskow, 83, confirmed Kolliker’s observations on 
the rabbit by finding on the tenth day evidences of separation of the 
