Tatami (Japanese armour) the other related parts of a full suit of Japanese armour. Collapsible head protection such as "" and other collapsible armor are also "tatami" armor; a traditional kabuto could also be part of a tatami gusoku. Tatami armour was lightweight, portable, convenient for transportation, and they were manufactured inexpensively for the ashigaru light infantry. Tatami armours were worn by all samurai classes from the highest class to the lowest class. The higher class samurai wore elaborate armour while the lower class samurai and retainers wore simpler versions. In his book "Arms and Armor of the Samurai: The History of Weaponry
Supernumerary body part considered to have lost much or all of their original function through evolution. These body parts can be classed as additional to the required functioning of the body. In human anatomy the vermiform appendix is sometimes classed as a vestigial remnant. Prosthesis is an artificial extension that replaces a body part, and cybernetics is the study of computer technology in relation to organisms which can include replacement or additional body parts. Body integrity identity disorder (BIID) is a psychiatric disorder in which a person thinks that they have one or more additional limbs than they should, despite having two arms