The figure shows a cross section of the spinal cord with letters. P is the outer part. Q is the butterfly shaped inner part. R is a swelling on the root that enters the back of the cord. S is the root that leaves from the front of the cord. Which option names them correctly?

Fig. 1: A cross section of the spinal cord with letters. P is the outer part. Q is the butterfly shaped inner part. R is a swelling on the root that enters the back of the cord. S is the root that leaves from the front of the cord.