It seems to me, that the artist who created the tablet in question was attempting to show a similarity but also a difference in the the two beings.

For one, the being on the right has no arms. It is hard to even identify it as a 'being', unless one sees the intention of the artist.

This may sound strange, but I can feel the struggle the artist hard, attempting to represent the being on the right properly, so that would be understood.

He added the 'second leg' as an afterthought feeling the 'being' appeared too 'serpent' like. Which may very well have been his intention but perhaps he hid it, or utilized the 'second leg' as cover for the Serpent.