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