There is a wicked paper out in PLoS ONE on how bats can actually use their uropatagia and tails to get a little extra lift during slow flight and launch. The paper is freely available (like all PLoS papers) here.
On the whole, the launch in Myotis works about the same as in Desmodus, but I do note one really neat difference: if you take a look at the figure I've pasted here from Adams et al. (2012), you'll note that in the first panel (bottom) the bat is pushing off at the wrist followed by the wing fingers. It's actually unfurling the wing part of the way early on (instead of late, as in Desmodus) and letting the highly compliant fingers in the wing bend to produce a pushing surface. That's not just bending at a joint, mind you, that's the actual bone that's flexing. Spectacular stuff.
This is not the first time that bat tails have been implicated in flight control. Another paper, also in PLoS ONE predicted the role of the tail in flight control previously (Gardiner et al., 2011). It's a nice little theoretical paper and it is neat that a theory-based work and an experimental one on the same bit of morphology hit in back-to-back years.
If you want to check out what the vampire version of bat launch, you can turn your cursors here for the manuscript in the Journal of Experimental Biology (Schutt et al., 1997). You can also check out a video of a vampire bat running here.
Adams RA , Snode ER , Shaw JB (2012) Flapping Tail Membrane in Bats Produces Potentially Important Thrust during Horizontal Takeoffs and Very Slow Flight. PLoS ONE 7(2): e32074. doi:10.1371/journal.pone.0032074
Gardiner JD, Dimitriadis G, Codd JR, Nudds RL (2011) A Potential Role for Bat Tail Membranes in Flight Control. PLoS ONE 6(3): e18214. doi:10.1371/journal.pone.0018214
Schutt, W. A. Jr., Altenbach, J. S., Young, H. C., Cullinane, D. M., Hermanson, J. W., Muradli, F., and Bertram, J. E. A. 1997. The dynamics of flight-initiating jumps in the common vampire bat Desmodus rotundus. The Journal of Experimental Biology, 200, 3003-3012.