mus is the RTECS abbreviation for mouse. On some MSDS's, the abbreviation may also be used. mus is not a standard abbreviation "muscle" or "muscular". RTECS uses ims for "intramuscular". Additional Info: mus appears on MSDS's in the context of a lethal or toxic dose concentration. Examples of such concentrations include LD50 and LC50 values as well as related terms such as TDLo (toxic dose, low), LDLo (lethal dose, low), and LCLo(lethal concentration, low). In the following examples from actual MSDS's, "mg/kg" refers to the specified quantity (in mg) of the test chemical per kilogram (kg) of animal body weight: Orl-mus LD50 >40 g/kg IPR-mus 7,548 mg/kg (inhalation, mus) ORL-MUS 4 mg kg-1 LD50: (IMS,MUS) 1190 MG. In the examples above, ORL-MUS above refers to an oral exposure route in mice and (IMS,MUS) refers to intramuscular injection in mice. It is sometimes difficult to assess the relative risks of chemicals when one LD50 is given for inhalation and another is given for injection. One has to consider the plausible routes of entry. For example, exposure to a vapor is much more likely through inhalation than through ingestion or injection. MSDS Relevance: Animal test results do not always accurately assess the risks to humans, but even so, they are quite valuable for assessing the relative risks of chemicals in your workplace. The lower the LD50 or related value, the more toxic the material. Always read your MSDS to assess the hazards of a substance and to determine what engineering controls or personal protective equipment may be necessary to protect you from workplace exposure. See also: Molality, Myalgia, Subcutaneous