The common law crime of mayhem is defined as an act of maliciously disabling or disfiguring the victim. This is essentially the modern definition as well.
The actus reus for mayhem is that the defendant must commit an act that causes the victim an injury that either permanently disfigures him or disables him.
Disablement is defined as the loss of use of a major body part. See
Disfigurement is defined as the alteration of the victim’s face or body that changes his normal appearance. See
As far as the mens rea is concerned, it is actually not necessary in modern law to have intended to disable or disfigure the victim. As long as the defendant intended to injure the victim and disablement or disfigurement was the result of the defendant's act he can be convicted of mayhem.
Mayhem was a felony at common law and it remains so under modern law.