Toupee all the way down.

Sometime between the 1982 movie Star Trek II: The Wrath of Khan and the 1984 movie Star Trek II: The Search for Spock, Bill Shatner's toupee underwent a somewhat drastic change that isn't immediately noticeable. Whereas up to and including The Wrath of Khan, Shats wore a weave that simply sat on the top of his head, by The Search for Spock, the toupee went all the way down to the sides of the ears.

Star Trek II toup.

Why the change? Did Shats go bald at the sides too? Probably not. The change was likely brought on by Bill Shatner's other big 1980s project T.J. Hooker, which ran from 1982 to 1986. This series was heavily action-based, with Shatner running and jumping and fighting in almost every scene. The top-of-the-head weave was apparently just not strong enough for the task, and was likely far too unruly and difficult to style amidst all the action. Although Shats started the series with the old weave style, he soon changed. T.J. fans might be able to help us spot the exact episode when that change took place.

A weave is tied to existing hair. In Shats' case, that meant to the back and sides. But, as we've learned by a bit of reading out there on the web, such weaves place a strain on the existing hair and can actually cause further baldness because the real hair that serves as the anchor is constantly under stress.

Star Trek III toup.

So, the solution is to widen the surface area that the weave is attached to. By extending it down to the sides, Shats' toupee became far more resilient in the face of all that T.J. Hooker (and Kirk too) had to endure. The old toupee would never have been able to take that kind of a pounding!