Which nerve is NOT involved in the innervation of the diaphragm?

The subscapular nerve is not involved in the innervation of the diaphragm, making it the correct answer. The diaphragm is primarily innervated by the phrenic nerve, which originates from the cervical spinal cord segments C3, C4, and C5. This nerve is crucial for the motor control of the diaphragm, allowing it to function during respiration.

The intercostal nerves, which arise from the thoracic spinal cord segments, also play a role in providing sensory innervation to the diaphragm's lower pleural surface, though they do not directly innervate the muscle itself. The L1 nerve primarily serves the lower abdominal region and is not associated with the diaphragm's motor or sensory functions. Thus, the subscapular nerve, which innervates muscles in the shoulder region and is not anatomically related to the diaphragm, clearly does not participate in its innervation.