Mystici Corporis Christi §34

³⁴ That this Mystical Body which is the Church should be called Christ's is proved in the second place from the fact that He must be universally acknowledged as its actual Head. "He," as St. Paul says, "is the Head of the Body, the Church." He is the Head from whom the whole body perfectly organized, "groweth and maketh increase unto the edifying of itself."