Jörmungandr-Ouroborus, the Tesseract

Tesseract

According to legend, Odin threw the serpent Jörmungandr into the great ocean (primal void or akasha) surrounding the plane called Midgard. The serpent grew so large as to surround the Earth.

This tends to confirm the truism that Earth is encompassed by 4-D space-time -- exactly that which is represented by the tesseract.

Ouroborus

Jörmungandr is known in the Greek mythic  tradition as Ouroborus.  Both are commonly represented by a serpent biting (swallowing) its own tail.  Indeed, the name itself means "tail-eating," or self-devouring.  This is an apt description of what we see in the animated graphic at top left.

hypercube pendant

The deeper significance, hinted in the opening paragraph, is that our three spatial dimensions, plus the temporal fourth, constitute an eternal self-devouring subject which acts as our existential domain.
The photograph at left presents a three-dimensional object commonly presented in two-dimensions as a cross within a circle, known as the Sun cross, or Odin's cross.  It is used in astrology to represent the planet Earth.

"Since each vertex of a tesseract is adjacent to four edges, the vertex figure of the tesseract is a regular tetrahedron."  (source)