PhD Examinations
In PhD examinations within the British system, there are normally only two or three examiners, and the external examiner usually takes the lead in questioning the candidate in the viva voce examination which is the key stage of the assessment. In some other countries, e.g. Australia, New Zealand and India, externals commonly send their opinions by post, though there may also be a "local" external examiner who is present at the viva.
Read more about this topic: External Examiner