y _ ROOT OF THE LUNG. 939 
The bronchus in the root of the lung lies behind the great pulmonary vessels. 
The pulmonary artery occupies a different position on the two sides in relation to the 
main or undivided part of the bronchus. On the right side it is placed below 
it, whilst on the left side it crosses the bronchus and occupies a higher level in the 
pulmonary root. The two pulmonary veins on both sides lie at a lower level in the 
root of the lung than the pulmonary artery and bronchus, whilst ae upper of the 
two veins occupies a plane in front of the pulmonary artery (Fig. 632, p. 934). 
Distribution of the Bronchial Tubes within the Lungs.—The Aen lungs are 
not symmetrical ; the right lung is subdivided into three lobes, and the left lung is 
cleft into two lobes. The bronchi exhibit a corresponding want of symmetry. The 
right bronchus, as it approaches the pulmonary hilus, gives off two branches for the 
upper and middle lobes of the right lung respectively, and then the main stem of the 
tube enters the lower lobe. The left bronch us sends off a large branch to the upper 
lobe of the left lung, and then sinks into the lower lobe. The first branch of the 
right bronchus for the upper right pulmonary lobe leaves the main stem about one 
inch from the trachea. The first branch of the left bronchus, on the other hand, 
takes origin about twice that distance from the trachea. 
The relation of the pulmonary artery to the bronchial subdivisions is different 
on the two sides. On the right side it turns backwards to reach the posterior 
aspect of the bronchus below ‘the first and above the second bronchial branch. On 
the left side the pulmonary artery turns backwards above the level of the first 
bronchial branch. On the right side, therefore, the first bronchial branch is placed 
above the pulmonary artery, and in consequence it is termed the eparterial bronchus ; 
all the others lhe below slits artery, and are termed hyparterial bronchi. On ihe 
left side there is no eparterial branch; they are all hyparterial. 
When the main stem of the bronchus is followed into the inferior lobe of each 
lung, it is seen to travel downwards and backwards in the pulmonary substance 
until it reaches the thin back part of the base of the lung which lies between the 
diaphragm and the thoracic wall, and there it ends. As it proceeds through the 
inferior lobe it gives offa series of large ventral and a series of smaller. dorsal 
branches. Asa rule these are three in number in each case, and the dorsal and 
ventral branches do not arise opposite to each other, but alternately, one from the 
back, and then another, after a slight interval, from the front of the tube. The 
first hyparterial division on each side (z.e.'the branch to the middle lobe of the right 
lung and the branch to the upper lobe of the left side) is generally regarded as the 
first member of the ventral group. 
It was Aeby who first recognised the existence in each lung of a main or stem bronchus 
giving off a ventral and dorsal series of branches, and who drew the distinction between the 
eparterial and hyparterial bronchial branches. A consideration of these relations led this author 
to conclude that the eparterial bronchus and the upper lobe of the right lung have no morpholo- 
gical equivalents on the left side of the body. In other words, he was led to believe that the 
middle lobe of the right lung is the homologue of the upper lobe of the left lung. Hasse, who 
has also investigated the subject, endorses this view, with certain modifications “and additions, 
and the hy pothesis, either in its original state as pre sented by Aeby, or as subsequently modified 
by Hasse, has been very generally accepted by anatomists. More recent research, however, has 
seriously affected the stability of this conclusion. Narath contends that the distinction between 
the eparterial bronchus of the right side and the hyparterial bronchi of both sides is not one of 
fundamental importance, and further, that a branch which arises from the first hy parterial 
bronchus on the left side and turns upwards into the apex of the left lung is the direct equi- 
valent of the eparterial bronchus of the right side. This he terms the apical bronchus, and he 
believes that it represents the first dorsal branch of the left stem bronchus. Huntington, in a 
very convincing paper, strongly supports the contention of Narath, and holds that, except “ for 
purposes of topography, we should abandon the distinction between eparterial and hyparterial 
bronchi.” With Narath he regards the eparterial bronchus as a secondary branch which has 
migrated in an upward direction on the main stem. According to Huntington, therefore, Aeby’s 
proposition should be amended as follows :— 
Right side. Left side. 
Upper 4 middle lobe = Upper lobe. 
Lower + cardiac lobe ss Lower lobe. 
‘The cardiac lobe mentioned in this table is the occasional azygos lobe to which reference has 
already been made, and it is interesting to note that, whilst the lobe in question as a separate 
entity is rarely seen in the human “lung, the bronchus which corresponds to it is always 
