In As You Like It, who are "mannish cowards" and how do they hide their cowardly nature?

This quote is said by Rosalind in Act I scene 3, and comes
as part of her speech when she plans to disguise herself as a man as she and her cousin,
Celia, talk about their escape from court to the Forest of Arden to look for Rosalind's
father. Rosalind is afraid of what could happen to them, as two young, beautiful maidens
alone, and in particular is wary of the possibility of being raped. To protect them, she
feels disguising herself as a man would present the image at least of male bravery, even
if it covers over female fear. Note what she says:

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A gallant curtal-axe upon my
thigh,

A boar-spear in my hand, and in my
heart,

Lie there what hidden woman's fear there
will,

We'll have a swashing and a martial
outside,

As many other mannish cowards
have

That do outface it with their
semblances.

Rosalind thus
draws a parallel to herself an to other real men, who appear to be big, strong and brave
on the outside, but are actually cowards on the inside. By adopting a "swashing and
martial outside," Rosalind will, like these "mannish cowards," be able to present
outwardly the appearance of a warlike and fearsome individual which will hide her fear
and lack of bravery on the inside. Note how this quote ties in to the ubiquitous theme
of appearances vs. reality, as Rosalind deliberately plans to disguise herself as
something she is not so others will think she is not what she
is.