Explanation:
The correct option is 'a'. The forearm has superficial, deep, and dorsal compartments. The deep volar compartment contains the flexor digitorum profundus (FDP), flexor pollicis longus (FPL), and pronator quadratus. During a volar fasciotomy (typically via a Henry or modified Henry approach), after opening the superficial fascia, the surgeon must explicitly dissect deeper and incise the epimysium covering the FDP to adequately decompress the deep compartment.

Reference: Gelberman RH, Zakaib GS, Mubarak SJ, Hargens AR, Akeson WH. Decompression of forearm compartment syndromes. Clin Orthop Relat Res. 1978;(134):225-229.