How Node.js emitter works? Understand passing arguments

I don't understand how the function(msg)... is called with myEmmiter.emit.
How does the .emit('someEvent', ...) know that the argument 'the event was emitted' should be passed to function(msg)...?
Is there a way to see the emit method source?

const events = require('events');
var myEmmiter = new events.EventEmitter();

myEmmiter.on('someEvent', function (msg) {
  console.log(msg);
});

myEmmiter.emit('someEvent', 'the event was emitted');

via rafr3