18 The Development of the Lungs 
on the stem bronchus. Of the four series, the primary, external, and 
posterior are the most important and are extensively developed, forming 
the principal bronchi of the adult lung. On the other hand, the anterior 
and internal proliferate to some extent but do not form extensively 
developed branches of the adult tree and are, therefore, termed by 
d’Hardiviller accessory bronchi using a similar nomenclature with a dis- 
similar meaning from Aeby and Narath. The further growth of the 
tree after the origin of the principal bronchi by collateral ramification, 
is by unequal dichotomy at first, and later, equal dichotomy. The pro- 
cesses differ with the different primary bronchi and appear earlier in the 
sheep than in the rabbit. The cardiac bronchus, according to d’Hardi- 
viller, arises from the stem bronchus and, in this animal, remains inde- 
pendent. In the sheep, it emigrates on to the 1st lateral bronchus. 
The bronchus on the left side, he believes, always originates on the stem 
bronchus and wanders onto the 1st lateral thus forming the Bronchus 
cardiacus of Hasse. In the rabbit, d’Hardiviller finds the eparterial 
bronchus originating on the right side by collateral ramification, but 
unlike other investigators, he believes there is also an eparterial bronchus 
on the left. It appears on the 13th day and in 24 hours begins to degen- 
erate and remains as a solid epithelial mass in connection with the 
mother bronchus. In consequence of his belief of the presence of this 
left eparterial element, d’Hardiviller thinks Aeby’s classification of the 
lungs of mammals is only of secondary value. It also emphasizes its 
independent character and forces him to conclude that it is independent 
of Narath’s apical bronchus as it is not a lateral branch of the first 
ventral bronchus. 
d’Hardiviller’s series of papers was interrupted by the appearance 
of a study by Nicholas and Dimatrova, 97, upon the development of 
the lungs in sheep by the Born reconstruction method in which they sup- 
ported, in most respects, his observations. In an embryo of 5 mm. they 
find the main bronchi appearing as asymmetrical buds on the lateral 
faces of the anlage. In their later growth, this asymmetry is exaggerated. 
After the origin of the primitive pulmonary sacs two buds appear on 
their lateral walls (embryo 9 mm.) representing the first two lateral 
bronchi while simultaneously the tracheal bronchus is seen as an elon- 
gated projection on the right side of the trachea. No trace of a sym- 
metrical bronchus, however, is found on the other side. They regard 
this element as being entirely independent of the bronchial system which 
must be regarded as a supernumerary bronchus originating from the 
future trachea just as the collateral bronchi are formed from the stems. 
The collateral bronchi, of which there are three sets, a lateral, a dorsal, 
