Ouroboros 

 

"self-reflexivity or cyclicality, especially in the sense of something constantly re-creating itself, the eternal return" - Wikipedia

 

 The Mind is a great Serpent (Dragon) with it's tail in it's mouth. (Ouroboros)

Also, it is Representative of the cycle of the Sun and Zodiacal progression back to its start...Aries. This can also be interpenetrated as a veil. It, in my opinion, can be considered a type of "star gate" and one must break through it to reach the divine or to progress to the highest of spiritual levels.