Ans. a (Opening the lower jaw) (Ref. Reddy's essentials of FMT 28th /141)Rigor mortis is tested by trying to lift the eyelids, depressing the jaw, and gently bending the neck and various joints of body.Rigor mortis (RM) # Individual cell death takes place in this stage# Occurs due to lack of 02 and ATP.0# When the levels of ATP are reduced to critical levels (85% of normal), rigor starts to occur.# The rigidity of muscle is maximum when the level of ATP is reduced to 15%.# When the lactic acid cone, reaches a level of 0.3%, muscle go into irreversible state of contraction - rigor mortis.# Nvsten's rule: RM does not start in all muscles simultaneously.# It first appears in involuntary muscles; the myocardium becomes rigid in an hour.# Follows proximo-distal progression.# It begins in the eyelids, neck and lower jaw and passes upwards to the muscles of the face, and downwards to the muscles of the chest, upper limbs, abdomen, lower limbs and lastly in the fingers and toes.# It always sets in, increases, and decreases gradually.# It is independent of the integrity of nervous system.# It does not occur in fetus < 7 months.# Cutis anserina/goose skin due to erector pilae muscle rigor.12# Time of onset:- In india, it begins 1-2 hrs after death and takes further 1-2 hrs to develop.- In temperate countries, it begins in 3-6 hrs and takes further 2-3 hrs to develop.# Duration of rigor:- In india, usually it lasts for 24-48 hrs in winter- And 18-36 hrs in summer.- In temperate regions, it lasts for 2-3 days.# It appears early, is of short duration in deaths due to:- OP poisoning - TB - Cholera - Typhoid - Lightning- Cancer - Cut-throat - Firearm - Electrocution - Strychnine poisoning# Its onset is delayed in deaths due to: Q- CO poisoning - Asphyxia - Severe hemorahge - Apoplexy- Pneumonia - CNS diseases causing muscle paralysis - Perfusion with normal saline.# It may disappear very rapidly in deaths due to:- Widespread bacterial infection, e.g., gas gangrene.# It may be absent in deaths due to:- SepticemiaTraitRMCadaveric spasmProductionFreezing and exposure to temp > 65degC produce rigorCannot be produed by any method after deathMechanismKnownNot clearly knownPredisposing factorsNoneSudden death, excitement, fear, exahaustion, nervous tensionTime of onset1-2 hrs after deathInstantaneousMuscles involvedAll (voluntary and involuntary)Usually restricted to single group of voluntary musclesMuscle stiffeningNot marked; moderate force can overcome itMarked; very great force required to overcome itMolecular deathOccursDoes not occurBody heatColdWarmElectrical stimuliMuscles do not respondMuscles respondMedicolegal importanceIndicates time of deathIndicates mode of death, i.e., suicide, homicide or accident.