The Earth Dragon Statues (土龍像 Doryuuzou) are save points used in Ninja Gaiden (Xbox), Ninja Gaiden Black, Ninja Gaiden Sigma, Ninja Gaiden Sigma Plus, Ninja Gaiden: Dragon Sword, Ninja Gaiden II, Ninja Gaiden Sigma and Ninja Gaiden Sigma 2 Plus, in addition to appearing as simply as decoration in Ninja Gaiden 3 and Ninja Gaiden 3: Razor's Edge.
There is a message engraved on the tablet in the dragon's mouth:
"The sacred underground paths of the Dragons record all that occurs in the world of men. We have not forgotten those who live on the surface of the Earth."
- Ninja Gaiden (first encounter with the Dragon Statues)
The Earth Dragon Statues record the happenings of the surfaces of the world, effectively functioning as save points for the player. In addition to this, they heal the wounds of the user once, losing their blue glow for that of a different colour.
It is unknown when or how the Earth Dragon Statues came to be, however they can be inferred to be the will of the ancient Dragons who've retreated from the world, as they record the events in the surface of the earth.