Looking at the text with an astrologically trained eye, the Dragon appears to be none other than the lunar nodes themselves. The lunar nodes are not planets. They are points in space indicating the intersection of two orbits, the points where the orbit of the Moon crosses the ecliptic. The north node (“dragon’s head”) is where the moon crosses from south of the ecliptic to north of the ecliptic. The south node (“dragon’s tail) is where it crosses from north of the ecliptic to south of the ecliptic. Their glyph (symbol) recalls the tail-eating dragon in form:
The function of the Lunar Nodes in astronomy is to predict the path of the annual eclipses through the constellations. Eclipses occur only near the lunar nodes. Solar eclipses occur when the passage of the Moon through a node coincides with the new moon; lunar eclipses occur when passage coincides with the full moon.