Editing Lung (section)

====Fissures====
The fissures are formed in early [[prenatal development]] by invaginations of the visceral pleura that divide the lobar bronchi, and section the lungs into lobes that helps in their expansion.<ref name="Koster">{{cite journal |last1=Koster |first1=TD |last2=Slebos |first2=DJ |title=The fissure: interlobar collateral ventilation and implications for endoscopic therapy in emphysema. |journal=International Journal of Chronic Obstructive Pulmonary Disease |date=2016 |volume=11 |pages=765–73 |doi=10.2147/COPD.S103807 |pmid=27110109|pmc=4835138 |doi-access=free }}</ref><ref name="Lung fissures">{{cite web|last1=Hacking|first1=Craig|last2=Knipe|first2=Henry|title=Lung fissures|url=http://radiopaedia.org/articles/lung-fissures|website=Radiopaedia|access-date=8 February 2016}}</ref> The right lung is divided into three lobes by a '''horizontal fissure''', and an '''oblique fissure'''. The left lung is divided into two lobes by an oblique fissure which is closely aligned with the oblique fissure in the right lung. In the right lung the upper horizontal fissure, separates the upper (superior) lobe from the middle lobe. The lower, oblique fissure separates the lower lobe from the middle and upper lobes.<ref name=GRAYS /><ref name="Lung fissures" />

[[Lung#Variation|Variations]] in the fissures are fairly common being either incompletely formed or present as an extra fissure as in the [[azygos lobe|azygos fissure]], or absent. Incomplete fissures are responsible for [[collateral ventilation|interlobar collateral ventilation]], airflow between lobes which is unwanted in some [[lung volume reduction]] procedures.<ref name="Koster" />