*Calpurnia seemed to know all about it. She was a less than satisfactory source of palliation, but she did give Jem a hot biscuit-and-butter **which** he tore in half and shared with me.*
*Although his back was to us, we knew he had a slight cast in one of his eyes **which** he used to his advantage: he seemed to be looking at a person when he was actually doing nothing of the kind.*
Why is there no comma in front of "which" in both sentences?