The horizontal fissure divides the middle and upper |lobes| of the right |lung| and the upper and lower |lobes| of the left |lung|. The right and left |lung| feature fissures which divide the overall structures into smaller |lobes|. The left |lung| (the body's left, the viewer's right) has one horizontal fissure which divides it into two |lobes| (upper and lower). The right |lung| has one horizontal fissure and one |oblique fissure|, dividing the right |lung| into three |lobes| (upper, middle, and lower). Because of this third |lobe|, the right |lung| is larger than the left, extending further down in the abdominal cavity. The right and left |lung| are each enclosed in a pleural sac and are separated by the mediastium, a membrane which extends from the |vertebral column| in back to the |sternum| in front.
