Nope, definitely skeletal muscle. Pretty big one too... intimately involved in respiration (inspiration to be exact). Innervated by the phrenic nerve, which arises from spinal nerves C3, C4, and C5 (also innervates the parietal paricardium (covering of the heart) and the pleura on the mediastinal side (side of the pleural cavity of the lungs facing the compartment of the thorax where the heart is situated). Incidentally chronic and severe hiccups can be treated surgically by crushing or sectioning this very same nerve).