Woman:“The spinal transmission system is open. Preparing for connection.”
Reichu: :shiver: Entry plugs… The entry plugsystem is very interesting and unique, in a rather icky way. The Evas are living creatures, so they obviously didn't start out being able to house this long, cylindrical object in their upper body. The entry system is, in fact, the most basic (and intrusive) of the “modifications” made to them.
felineki: According to Sore o nasumono: Neon Genesis Evangelion Concept Design Works, a portion of the Eva's upper spinal column is composed of implanted “artificial bone” . The light bone-colored plates you see exposed in Sho's upper back here correspond with a sketch included in the book illustrating the artificial spine section. According to the sketch, this section runs from the base of the skull all the way to past the bottom of the shoulder blades! This section of spine is also partially exposed, whereas the rest of the body still has skin.
Reichu: Speaking of skin, if you look closely here, you can actually see some that is exposed. (Brown, the typical Eva pigmentation.)
felineki: It seems possible that during the “creation” process of an Evangelion, the portion of spine that is to be replaced is simply ripped out and the artificial section shoved in and left exposed.
Reichu: Well, “ripped out” seems a bit harsh… It's done neatly enough that they probably did some kind of precision surgery. Not to mention the phony part would have to be properly articulated with the remaining genuine spine. But there are actually muscles that attach to one's vertebrae; how the hell did they deal with that?
felineki: The artificial section of spine does seem to be composed of “vertebrae” parts and have some degree of flexibility. The strangest feature would have to be the plug hole, which would seem to go completely through the spinal column. The entry plug is inserted at an approximately 45 degree angle (if some of the more accurate Evangelion models are any indication), which would bring the leading edge of the plug into or near the solar plexus region of the Eva, coming into contact with, or possibly even penetrating into, the core. (More evidence of the plug's proximity to the core appears in later episodes.)
Reichu: Additionally, I would guess that there is an interior part to the entry system that actually receives the plug. Otherwise, they'd be sticking it straight into the Eva's thoracic cavity, which could potentially be rather messy…
felineki: The top (or back) of the plug settles flush with the artificial spine at around the base of the neck. The plug likely interfaces with the equivalent of the spinal cord in this region, theoretically allowing control of most of the muscles of the Eva's body.
Reichu: Not to mention the complete mutilation of the Eva's spine is certainly the fundamental means by which Nerv keeps them under control. If your brain is severed from your central nervous system, have a fun time moving the rest of your body. (Would that make the Evas glorified quadriplegics?) But as we saw back around 274, there are ways around this. ;;>
Also notice how the artificial vertebrae are mechanically integrated with the outer armor(the top and bottom entry plug lid, and such)… Speaking of which, is it just me, or is it the plug cap that pushes Shogouki's head forward when it rises?
Z Metalla: To me, the entry plug has always looked a bit like a tampon applicator… And the entry plug's placed in an orifice inside the Eva. Hmm! Isn't that a nice, disturbing tidbit? ^_^
Reichu: Even more disturbing, you're not the only one to have noticed this correlation. Consult ReDeath for one of the more tasteful examples. Consult this (NSFW) for a more direct treatment. (Squeamish people, please stay far away!)
