How to find method implementation in numpy repo

I just read about the Box-Mueller approach for generating normal random variables and want to see if the method in numpy python uses the same approach. To this end, I want to look at the source code. I've been combing through the GitHub repository but haven't had any luck yet. The folder "random" seems to not have the code I'm interested in. In particular, I want the code that is invoked when calling -

import numpy as np
rand = np.random.normal(size=10)

Is anyone able to point me to this part of the code and generally explain how to effectively perform these kinds of searches.