The Clerk of the House of Commons is both the house's chief adviser on matters of procedure and chief executive of the House of Commons. She or he is a permanent official, not a member of the house itself. The Clerk advises the Speaker on the rules and procedure of the house, signs orders and official communications, and signs and endorses bills. The Clerk also chairs the Board of Management, which consists of the heads of the six departments of the house. The Clerk's deputy is known as the Clerk Assistant. Another officer of the house is the Serjeant-at-Arms, whose duties include the maintenance of law, order, and security on the house's premises. The Serjeant-at-Arms carries the ceremonial mace, a symbol of the authority of the Crown and of the House of Commons, into the house each day before the Speaker, and the mace is laid upon the table of the house during sittings. The Librarian is head of the House of Commons Library, the house's research and information arm.