9.3. Hilum of Each Lung
There is a hilum of the left lung and a hilum of the right lung, as shown in the accompanying diagram. The hilum is also called the root of the lung, and it is the location where the pulmonary blood vessels enter and leave the substance of the lungs. It is also (approximately) the position where you can see the primary bronchus on each side (and in some instances where the primary branches bifurcate to become the secondary bronchi)(see Section 9.4).
Note that the view of each hilum depends upon the exact location of the sagittal plane (from which the view has been sketched). For example, if the sagittal plane was at a more lateral position, deeper in the lungs, one would see that the pulmonary vessels had divided into more smaller branches, and one would see the secondary bronchi clearly. Note also that there are two pulmonary arteries but four pulmonary veins (as can be seen entering/leaving the heart).