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Photographs and corresponding illustrations of three categories of fibre characterized according to their origin and location (arrows). The muscle fibres simultaneously originated (a) from the anterior and posterior aspects of the duct, (b) from the anterior and superior aspects of the duct and then inserted into the anterior aspect of the duct, and (c) from the posterior and inferior aspects of the duct. Ant., anterior; Post., posterior; Sup., superior; Inf., inferior.
