WW24 CREW TAXIES PAST RWY HOLD SHORT LINE AT MYNN.

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WHILE TAXIING FOR DEP; WE WERE INSTRUCTED TO 'CROSS RWY 14; HOLD SHORT OF RWY 8.' AFTER XING RWY 14 AND TURNING L ONTO PARALLEL TXWY; I FAILED TO STOP SHORT OF THE HOLD SHORT LINES FOR RWY 8. AFTER STOPPING; I REALIZED THE NOSE OF OUR ACFT WAS EXTENDING INTO THE RWY; SO I ELECTED TO EXPEDITE ACROSS THE REST OF THE WAY AND CLR THE RWY. THERE WAS NO ACFT ARRIVING OR DEPARTING RWY 8 AT THE TIME; ALTHOUGH IT WAS ACTIVE; AS WAS RWY 14. THE TXWY WE WERE ON CROSSES RWY 8 AT THE EXTREME DEP END; REPRESENTING THE LAST 75 FT OF RWY 8. PART OF THE PROB AROSE BECAUSE MY MENTAL PICTURE OF WHERE RWY 8 INTERSECTED RWY 14 WAS INCORRECT. THIS COULD OBVIOUSLY HAVE BEEN AVOIDED IF I HAD INSTRUCTED THE PNF TO HAVE THE ARPT DIAGRAM AT HAND AND MONITOR OUR PROGRESS WHILE TAXIING. THE AWARENESS THAT WE HAD TAXIED TOO FAR CAME LATE; PARTLY DUE TO THE UNKEMPT NATURE OF THE DEP END OF RWY 8 (GRASS GROWING UP THROUGH CRACKS; FADED; OLD MARKINGS; ETC). THIS EVENT COULD HAVE BEEN AVOIDED COMPLETELY HAD I INSISTED THAT BOTH OF US MAINTAIN VIGILANCE OUTSIDE THE COCKPIT WHILE TAXIING AT A RELATIVELY UNFAMILIAR ARPT; AND LEAVE VARIOUS COCKPIT DUTIES UNTIL WE HAVE CEASED MOVING.