Mike Turner explains the construction of the viola:
and the differences between a viola and a violin:
He also discusses the character of the instrument:

There are normally four strings on a viola, tuned to C3, G3, D4, A4

Scroll = curved end of the viola
Peg = device for tuning strings (by altering their tension)
Peg box = the frame that holds the pegs
Nut = the ridge on the edge of the peg box that supports the strings
Neck = the extension from the body of the viola that supports the fingerboard
Fingerboard = the wooden surface against which the fingers are pressed f-hole = openings in the body of the viola from which the sound emerges
Bridge = a shaped piece of thin wood supporting the strings and through which sound is transmitted to the body
Tailpiece = anchors the strings
Chin rest = shaped wooden rest
End pin = attaches tailpiece to body of instrument
Tip = the end point of the bow
Hairs = the stretched horsehair (or other material) which normally makes contact with the strings
Wood = flexible, and usually supports the hairs
Frog = the heel of the bow.

The Orchestra: A User's Manual is a free resource and will remain so. It still receives between 8,000 and 16,000 unique visits per month from all over the world. See the testimonials. Thanks to all the donations, I have been able to create this responsive re-design. But the movies and sound clips recorded in 2004 do show their age. I would really like to re-record everything and add many more techniques, especially for solo and ensemble writing. I estimate this will cost around £30,000. If you know a source of such funds, please contact me: a.hugill [at] bathspa.ac.uk