The History of Terriers
French Eching showing Earthdogs c 1560
Terriers were first classified as such by Dame Juliana Berners in 1486 AD, calling them 'Teroures'. This wonderful French etching from around 1560 AD demonstrates that for centuries certain types of scent hounds dug into tunnels and underground lairs to find and hunt prey that lived beneath the ground. As these seem to be long low-slung dogs, with deep chests, they appear to be similar to 'the 6 best earth dogges in Argyll (Scotland)' which James 6th of Scotland sent to France in 1600 AD.
Terrier Hunting with net c 1584
In 1570, Dr. Johannes Caius called the type of scent hound that follows its prey beneath the ground Terrier in his classification that was written in Latin and translated into English by A Fleming in 1576 AD. The original translation of this important work is difficult to read to be printed in its original form.
Dr Caius extract on Terriers
So it appears here as my interpretation in modern English:
'There is another sort of Scent Hound that only hunts the fox and the grey badger. These are called Terriers because they (after the manner and custom of ferrets, in searching for rabbits) creep into the ground, and frighten by nipping and biting the fox or the badger. Alternatively these terriers either tear them into pieces with their teeth in the bosom of the earth, or else haul and pull them, by force, out of their lurking angles, dark dungeons, and close caves, or at least through conceived fear, drive them out of their burrows. So the fox or badger is compelled to bolt, being desirous of the next, albeit not the safest refuge, the fox or the badger is otherwise taken and entrapped with snares and nets lain over their holes'.
References and Further Reading
 Dr John Caius, Of Englishe Dogges: The Diuersities, the Names, the Natures, and the Properties, trans. Abraham Fleming (London, 1576), 36. Originally published in Latin in 1570 as Johannes Caius, De Canibus Britannicis.
 Colonel E. D. Malcolm C. B. of Poltalloch, 'The West Higland White Terrier' Cassell's New Book of the Dog' by Robert Leighton assisted by eminent authorities on the various breeds Published by The Waverley Book Co Ltd Vol 111, Chapter XLI Page 391
Also published in 2015 as"The Historical Function of Terriers" by Jane Harvey in 'The Talkabout" the Official Publication of the Australian Terrier Club of America 2015 Issue 2 Pages 36 - 37
See also Jane Harvey, DVD "Terriers Then & Now" (Rangeaire Vision 2002, 2004) ISBN 978-0-9804296-4-0