Hutto & Myin, 2013, p. 12

once one abandons the idea that mentality is essentially content involving there is no a priori reason to suppose that cognition is an exclusively heady affair. Rejection of [Content Involving Cognition], and along with it representationalism, thus provides the cleanest and clearest motivation for thinking that cognition is fully embodied and embedded, and not merely embrained.

I see a few gaps here.

1. Suppose you think, as I do, that cognition does involve content.  Still that provides no a priori reason to think that cognition is embrained.  One would presumably also need some empirical work to establish that content (typically) occurs in brains.

2. Grant that once one abandons the idea that mentality is essentially content involving there is no a priori reason to suppose that cognition is an exclusively heady affair.  That leaves open the possibility that there is an a posteriori reason to suppose that cognition is an exclusively heady affair.

3. Grant that cognition is not essentially content involving.  How does that tell you what the realization base of cognition is?  Presumably you would need some account of what cognition is, then something like empirical evidence about the realization base of that cognition.