Sentence:  One growth <WSD>center</WSD> in a short bone - distal phalanx of the second finger - was chosen as an example for discussion here , primarily because epiphyseal diaphyseal fusion , the maturity indicator for Completion in long and short bones , occurs in this center for girls near the menarche and for boys near their comparable pubescent stage . 
Meaning of the word marked with <WSD> tags:  an area that is approximately central within some larger region