Yes, SARTORII is a Scrabble word!

Letter values in Scrabble US: S 1, A 1, R 1, T 1, O 1, R 1, I 1, I 1.

Is it a valid word?

SARTORII is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a muscle in the thigh that helps to rotate the leg into the sitting position assumed by a tailor; the longest muscle in the human body

Also: sartorius muscle, musculus sartorius.