8 The Development of the Lungs 
of the pulmonary system in man, differs from His in looking upon the 
first anlage as symmetrical. Its subsequent asymmetry Minot believes 
is due to the unequal development of the heart. 
In sheep, Nicholas and Dimitrova, 97, find by the reconstruction 
method in an embryo of 5 mm. the main bronchi resulting not from a 
bifurcation of the primitive pulmonary projection, but as asymmetrical 
buds on its lateral face. Later stages, 7-9 mm., show an exaggeration 
of the precocious asymmetry as the right side is considerably more 
developed than the left, and the two primitive bronchi with the trachea 
form an inverted T. 
Narath, o1, followed the development of the lungs in rabbits and 
guinea pigs. In the latter, the development begins as a lateral flattening 
of the head gut just under the Fundus branchiales. This process con- 
tinues until the lumen of the head gut forms a sagittal fissure just above 
the lower anlage, which, as it passes upwards, soon resumes its rhom- 
boidal form. The ventral groove deepens and thickens, while, at the 
same time, the dorsal groove becomes narrower. Lungs and trachea 
arise from the ventral, while the dorsal part yields the cesophagus. 
Somewhat later a longitudinal furrow separates the two and the pro- 
jection at the most caudal portion of the ventral groove, forming the first 
unpaired anlage of the lungs, shows a slight asymmetry as the right 
side is somewhat larger than the left. The lung anlage increases in 
size, ventrally, but even more markedly to the right and left. These 
two outgrowths, the anlage of the bronchi, show different relationships, 
as the right bends dorsally and caudally, while the left remains practi- 
cally transverse. About this time begins the separation of the trachea 
from the cesophagus, which proceeds in a caudocephalic direction until 
the mesoderm surrounding the lung sacs not only projects into the cavity 
of the ccelom, but also passes in and separates the respiratory from the 
digestive portion of the head gut. The end of the lung sacs dilate, while 
still maintaining a marked asymmetry and, as this takes place, they ex- 
tend dorsalward and embrace the cesophagus. In the development of the 
cat’s and rabbit’s lung, the transformation in general agrees with the 
conditions in the guinea pig so that Narath finds himself in accord with 
the earlier researches of Ko6lliker and Uskow, who also worked on the 
latter animal. Somewhat later Weber and Buvignier, 03, in a com- 
parative study of the origin of the lungs, especially in Muinopterus 
Schreibersii, followed, by the reconstructive method, the lateral flatten- 
ing of the post branchial region of the head gut. They describe a bran- 
chial crest, which descends from the last pair of gill pouches and ter- 
minates just before reaching the region in which the pulmonary appa- 
