If it is possible, it is best to have the grain of the wood running parallel with the wrist on the stock.
If the grain is running parallel with the bore it will be weak in the area of the wrist because the boundaries between the grain will be in shear when the gun is being loaded or fired. The sear strength of the boundary layers is always weaker than the strength in the direction of the grain.
An example of a weak grain pattern can be seen on the Tennessee rifle I built from a piece of walnut.
In this guns case, because of the extra long trigger plate and tang on the barrel I was able to install two screws that go down thru the wrist. With the two screws threaded into the trigger plate it basically makes a sandwich with the steel tang and trigger plate being the bread and the wood between them being the filling. You can see the head of the rear tang screw just to the right of the rise to the comb of the stock.
Doing this increases the strength of the wrist tremendously but when all is said and done, I would have much rather had the wood grain running parallel with the wrist.
(Yes, you see the remains of a flintlock pan supporting the percussion drum on the lock. This is a Siler kit flintlock lock and I messed up the pan's bridle so I decided to "update" the lock to a percussion lock for this rifle.
That would explain why the tail of the lock isn't like most Tennessee rifles. "That thar lock were an ol' Pennsylvania lock that were used fer building that thar rifle gun. At's why she's a lookin funny ta ye." )