Source:
http://dulcimer.net/store/
http://www.causewaymusic.co.uk/usmtd.html
The common dulcimer is very similar in structure and design to the cymbalum, and may thus be regarded as a kind of clavichord (of the piano family). Each pitch has its own strings which are pretuned and the pitch of each string remains unchanged during playing. It may be envisaged as a piano without keys, while triggering sound is done by hand held hammers, played directly on the strings. Historically the piano may be regarded as a later devleopment of the dulcimer, they main difference that keys on a keyboard were introduced.
Source:
http://dulcimer.net/store/
http://www.causewaymusic.co.uk/usmtd.html
The narrow (or teardrop dulcimer, or mountain/Appalachian dulcimer) has fewer strings, and perhaps the name is confusing as in construction it is more similar to the zither than the cymbalum, while the strings are plucked, not hit. It also has frets, which the common dulcimer does not have.
The teardrop dulcimer came into use around the 1800s among the Irish and Scots, and must thus be a later variation of the cymbalum which was invented around the 1100s (or according to some even as early as 2000 years ago).
Source:
http://www.marcillewallis.com/marcille.htm
http://www.earlymusic.co.uk/general/prod_6.htm
http://www.youtube.com/watch?v=s9HnRZlMiKQ