ELASTIC SPRING MECHANISM
a structure consisting of thin spring-like modified portions of the parapophysis of the 4th vertebrae (Müllerian process) which are attached to the skull by muscles and to the gas bladder. When the muscles contract and relax, the resultant vibrations in the gas bladder produce a growling sound, e.g. certain Clariidae and other catfish families. See also Müllerian process and Müllerian protractor. See also drumming muscle and protractor post-temporalis mechanism