If you start to study Evas in earnest (e.g., for the purpose of drawing them), you may begin to notice that not much thought went into many aspects of the design. The core is one such item. On a good day, they’ll at least put the core in the solar plexus area. (I mean, if you look under the sternum at the open part of the rib cage, it looks like you can fit a big red ball there, right?) On a bad day (*cough*most of EoE*cough*), they’ll just have the core clip straight through the sternum and ribs, even though this makes absolutely no visual or anatomical sense and there is no reason whatsoever to do it.
I've been a good girl all these years, fastidiously placing Eva cores in the solar plexus region, since that option has at least some plausibility. And yet it pains me to acknowledge that it still has its problems. Evas have “suspiciously” hominid-like organ systems crammed into those lanky torsos of theirs, and there is evidence to suggest that they start off without cores as we know them. Perhaps this is because the core is an intrinsically artificial structure, or -- my preferred explanation -- because it only develops in the presence of the soul, which Evas do not receive until their bodies are fully grown. Either way, when the core is added, it is displacing whatever structures had originally been there. Cores aren’t small -- that’s a lot of disruption. Throw in the bulky entry plug housing unit, and you’ve got even more anatomy with nowhere to go.
To enumerate, here are some absolutely basic problems that come to mind:
1) The core takes up a significant amount of space that would otherwise be occupied by vital chest organs and associated blood vessels, nerves, etc. (Which Evas do have, regardless of how much they actually need them.) 2) It interferes with everything about the diaphragm. 3) It interferes with the attachment sites of the rectus abdominis. 4) The solar plexus is so named for a not-insignificant collection of nerves. These need to go somewhere.
In any event: branching my idiosyncratic naked Eva designs off into their own non-Eva thing -- a species called the Heledi -- for Daughters of Maruduk provides the perfect opportunity to address such niggling matters. I’ve taken the first step in this direction by attempting to reimagine what a humanoid rib cage might look like if it specifically evolved to accommodate a core.
Very, very distant evolutionary ancestors of the Heledi underwent a major endosymbiotic event with a mysterious crystalline, non-cellular organism (i.e., what would become the core). Multiple cores became a common feature of that planet’s multicellular life, integrated completely with the nervous and metabolic systems. With the development of complicated social animals, most of the body’s critical nuclear functions had become centralized to a single unusually large core, the few smaller cores that remained having since taken on specialized roles.
As my own alien race, Heledi internals can be designed with the core in mind, so no problems there. The rib cage does not merely provide space for the core -- it supports it, keeping it anchored in place. The inside of the ring-like structure is lined with bony struts that harmlessly weave into the nuclear crust as the core grows to its full size. The ribs are reinforced with a vertical strut (inspired by Sachiel) and have undergone significant fusion, providing further support. Lastly, the rib cage extends past the core caudally to provide attachment sites for the abdominal muscles.
At this point, I’m unclear about how breathing will be handled. My first thought is to make Heledi respiration more theropodian than mammalian, but I still need to research this and see what it will require from them anatomically.
N.B. The two corelets that are floating below the nuclear ring are an as-yet-unnamed mammary gland analogue.