When transistor Q1 is driven to {TAIL ~ a conducting condition}, current flows from the voltage source Vs, via line 11, through the lower winding L1 of {HEAD ~ the primary} of transformer T to ground via the now conducting transistor Q1 
When transistor Q1 is driven to { TAIL ~ a conducting condition } , current flows from the voltage source Vs , via line 11 , through the lower winding L1 of { HEAD ~ the primary } of transformer T to ground via the now conducting transistor Q1
OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH