Complex sentence: A disgruntled miner, Gwyllm Griffiths, volunteers for the experiment, enabling the professor to create a being with enhanced mental capabilities, and who, incidentally, begins growing an overdeveloped cortex and a "sixth finger" on each hand.
Split into simpler sentences: A disgruntled miner, Gwyllm Griffiths, volunteers for the experiment, enabling the professor to create a being with enhanced mental capabilities. Gwyllm soon begins growing an overdeveloped cortex and a "sixth finger" on each hand.