Sentence:  ... Yidinj has just one prefix "dja:-" 'in the direction of' .... There is a noun "djawa" 'mouth' in a number of neighbouring languages ... and it is likely that this developed into the prefix "dja:-". The semantic motivation would be the fact that Aborigines typically indicate direction by pointing with <WSD>pursed</WSD> lips (in circumstances where Europeans would extend a hand or index finger). 
Meaning of the word marked with <WSD> tags:  To press (one's lips) in and together so that they protrude.