Jerome
Catena Aurea · Lukasevangelium 2
And so it was, that, while they were there, the days were accomplished that, she should be delivered. And she brought forth her firstborn son, and wrapped him in swaddling clothes, and laid him in a manger; because there was no room for them in the inn.
(cont. Helvid.) From this Helvidiusd strives to prove that no one can be called firstborn who has not brothers, as he is called only-begotten who is the only son of his parents. But we thus determine the matter. Every only-begotten is firstborn, not every firstborn is only-begotten. We say not that he is first-begotten whom others follow, but before whom there is no one; (otherwise, supposing there is no firstborn but who has brothers following him, there are then no firstlings due to the priests as long as there are no others begotten;) lest perchance when no birth follows afterward, there should be an only-begotten and not a firstborn.