Sentence:  But at the end of the sitting , when Michelangelo showed him the quick , free drawings , with the <WSD>mother</WSD> roughed in , holding her son , the model grasped what Michelangelo was after , and promised to speak to his friends . 
Meaning of the word marked with <WSD> tags:  a woman who has given birth to a child (also used as a term of address to your mother)