Some time before the William Shatner School of Toupological Studies launched Shatner's Toupee, an amateur toupologist called "Nite Trek" was conducting toupological research and posting it on the "Trek BBS" Star Trek message board (see picture above). We certainly applaud and encourage such research, though we hope that if a touposcope was used, that adequate protection against toup-particle emissions was ensured.
The unusual image is from the first season Star Trek episode "Balance of Terror". The particular close-up shot of Captain Kirk represents, we believe, perhaps the single greatest lace malfunction in the entire series. Close attention to makeup and lighting would usually ensure that the lace line that anchored the front of (or frontal) toupee to Bill Shatner's head remained all but invisible. If we enhance an image from the scene, the line becomes even more prominent:
We have a description of this line from Star Trek producer Bob Justman in the book Inside Star Trek: The Real Story (see here for more):
"My gaze shifted to his (Shatner's) hairline. Examining balding actors' hairlines was a habit I'd picked up over the years. The 'lace' that anchored the front of his toupee glistened. I made a mental note of it to tell the makeup man about it before we filmed again."
One thing that Bill Shatner evidently soon learned after this incident was to avoid scrunching his forehead, which only helped to dislodge the fragile flap. As to why in this case the lace line was so low, we can only speculate. Perhaps this was the first appearance of a new toupee - Bill Shatner had two toupees on Star Trek as Bob Justman also noted in the aforementioned book:
"We had begun the first season with two new toupees for Bill because his own 'personal' ones were too ratty-looking. He would wear one toupee while the other piece was being cleaned in the makeup department...Each hairpiece cost $200, a pricely sum in those days."
Perhaps following this shot, the skin was cut back a little, while lighting and makeup likely did their best to make sure that such an incident never occurred again. As to why such a protruding skin was required at all, that likely has something to do with finding a smooth surface to paste the toupee on to. Bill Shatner evidently had a little hair on the front of his scalp that he may have been reluctant to shave off to provide such a surface directly under the toup.