Abstract
An Optomax Image Analyser has been used to carry out fibre-size analyses in six pairs of human recurrent laryngeal nerve and two pairs of recurrent nerves from adult giraffes. in every case the left recurrent laryngeal nerve was found to contain a greater number of large, fast-conducting fibres. Since this nerve is longer than the right, these findings may explain the simultaneous arrival of motor impulses to both sides of the laryngeal musculature.