Looking at Gemini´s spacesuit G-4C I always wonder how did they make the neck joint able to swivel, allowing the user to look at both directions? Wouldnt be easier to make a slightly bigger helmet (i.e. SK-1 for Vostok) with a large faceplate visor?
Let's find a bigger version of the image that you attach and blow it up:
As you can see, they used bearing with an arc rail to hold the umbilical in place. The outer ring of the bearing is attached to the collar of the suit, and the helmet slides into a locked position and attaches to the inner ring of the bearing. Similar bearings are still used on newer EVA suits in hips and gloves, and some newer designs to support future human exploration of Mars use even more of them at various angles (two in pairs at a canted angle to each other) to enable more natural joint movement.
See image gallery at the source of above image I crop (basically I found it by drag-dropping your image into Google Image Search's search bar and cropped from the highest resolution it found), and there's some more information regarding bearings on NASA's Learn About Spacesuits page.