Which extrinsic muscle is primarily affected first during rigor mortis?

Rigor mortis is the postmortem stiffening of the muscles due to biochemical changes in the muscle tissue after death. It typically begins an approximately two to six hours after death, starting with the smallest muscles first before progressing to larger muscle groups.

The eyelids are affected first during rigor mortis, which is observable as these muscles are smaller and have a faster onset of stiffness compared to larger muscles like the deltoid or the flexor digitorum. This phenomenon is significant in forensic examinations as it can assist in determining the time of death and the rigor mortis progression in the context of a post-mortem interval examination. The sequence in which rigor mortis occurs generally follows the order of muscle size and type, with the facial muscles, including those controlling the eyelids, being among the first to exhibit rigidity.

In contrast, larger muscles like the deltoid experience stiffness later in the process. Similarly, the orbicularis oris, while also a facial muscle, does not typically exhibit rigor mortis stiffness as early as the eyelids. The flexor digitorum, being a larger muscle located in the forearm, would also not be among the first affected. The understanding of these patterns is crucial in forensic