Which Lobes Does the Oblique Fissure Divide?
The lungs (pulmones) are paired, asymmetric organs of the thoracic cavity separated by the mediastinum. The oblique fissure is the primary structure establishing their lobar architecture. It is visible on all projections (anterior, posterior, and lateral).
- In the left lung — the organ consists of two lobes. The oblique fissure divides the superior lobe (lobus superior), occupying the upper regions of the thorax, and the inferior lobe (lobus inferior), whose main bulk is located posteroinferiorly.
- In the right lung — the organ consists of three lobes. Here, the oblique fissure separates the superior and middle lobes (lobus medius) from the inferior lobe.
Additionally, the right lung features a horizontal fissure (fissura horizontalis), which branches off the oblique fissure on the costal surface and separates the superior lobe from the middle lobe.
Surface Marking of the Oblique Fissure
The projection of the oblique fissure (fissura obliqua) is identical for both the right and left hemithoraces. Its topographical line runs across the following landmarks:
- Origin — posteriorly, at the level of the spinous process of the third thoracic vertebra (Th3).
- Course — the fissure runs obliquely downward and forward, curving around the chest wall along the costal surface, which lies against the ribs.
- Termination — anteriorly, at the sixth rib along the midclavicular line, at the junction of the bony sixth rib and its costal cartilage.
Topographical Relationship with the Horizontal Fissure
The middle lobe (lobus medius) is unique to the right lung, making the horizontal fissure a feature exclusive to the right side.
- Intersection Point — the horizontal fissure merges with the oblique fissure on the costal surface of the lung. Topographically, this point projects to the level of the fifth rib at the midaxillary line.
- Further Course — from its intersection with the oblique fissure, the horizontal fissure courses anteriorly, corresponding to the projection of the fourth rib, and terminates where the fourth costal cartilage attaches to the sternum.
Anatomical Context and Surfaces of the Lung
The lungs are paired organs located within the thoracic cavity. The lung tissue is elastic, spongy, and pinkish-gray.
Each lung features an apex (apex pulmonis), a base (basis pulmonis), and several surfaces:
- Costal surface (facies costalis) — apposed to the ribs.
- Mediastinal surface (facies mediastinalis) — apposed to the mediastinal organs.
- Diaphragmatic surface (facies diaphragmatica) — rests on the diaphragm.
The lung apex projects above the clavicles. The mediastinal surface contains the hilum of the lung (hilum pulmonis), through which the main bronchus, pulmonary artery, and pulmonary veins pass. Collectively, these structures form the root of the lung (radix pulmonis). The right dome of the diaphragm sits slightly higher than the left.