▁the ▁Under ground . ▁It ▁is ▁unique ▁in ▁having ▁two ▁different ▁routes ▁through ▁central ▁London ▁and ▁two ▁northern ▁branches . ▁Despite ▁its ▁name , ▁it ▁does ▁not ▁serve ▁the ▁northern most ▁stations ▁on ▁the ▁network , ▁though ▁it ▁does ▁serve ▁the ▁southern most ▁station , ▁, ▁as ▁well ▁as ▁ 1 6 ▁of ▁the ▁system ' s ▁ 2 9 ▁stations ▁south ▁of ▁the ▁River ▁Th ames . ▁There ▁are ▁ 5 0 ▁stations ▁in ▁total ▁on ▁the ▁line , ▁of ▁which ▁ 3 6 ▁have ▁platforms ▁below ▁ground . ▁ ▁The ▁line ▁has ▁a ▁complicated ▁history , ▁and ▁the ▁current ▁complex ▁arrangement ▁of ▁two ▁main ▁northern ▁branches , ▁two ▁central ▁branches ▁and ▁the ▁southern ▁route ▁reflect s ▁its ▁gen esis ▁as ▁three ▁separate ▁rail ways , ▁combined ▁in ▁the ▁ 1 9 2 0 s ▁and ▁ 1 9 3 0 s . ▁An ▁extension ▁in ▁the ▁ 1 9 2 0 s ▁used ▁a ▁route ▁originally ▁planned ▁by ▁a ▁fourth ▁company . ▁Ab andon ed ▁plans ▁from ▁the ▁ 1 9 2 0 s ▁to ▁extend ▁the ▁line ▁further ▁south wards , ▁and ▁then ▁north wards ▁in ▁the ▁ 1 9 3 0 s , ▁would ▁have ▁incorpor ated ▁parts ▁of ▁the ▁routes ▁of ▁two ▁further ▁companies . ▁From ▁the ▁ 1 9 3 0 s ▁to ▁the ▁ 1 9 7 0 s , ▁the ▁tracks ▁of ▁a ▁sevent h ▁company ▁were ▁also ▁managed ▁as ▁a ▁branch ▁of ▁the ▁Northern ▁line . ▁An ▁extension ▁of ▁the ▁Char ing ▁Cross ▁branch