Final answer:
Harrison's head strap is likely secured by a tied belt that fits into a cleft in the figure, functioning as a simple fastening mechanism.
Step-by-step explanation:
The question refers to a detail in a story where Harrison's head strap is mentioned. From the information provided, it seems that Harrison's head strap is secured by something that's indicated as a tied belt that hangs down. This tied belt likely fits into a horizontally carved cleft, which would function to keep the head strap in place. While the passage doesn't specify the exact mechanism, the description suggests a sort of clasp or notch system formed by the cleft and the belt, resembling a form of simple buckle or fastening arrangement.