=649.= The captain gives any desired special instructions to the guidon and sees that proper measures for security are taken. On dismounting, the first sergeant remains near the horses long enough to see that the designated noncommissioned officer is in charge and is making proper provision as regards the horses; he then joins the captain. Any sergeants who may be extra file closers without special assignment of duties join the captain; other extra file closers not specially assigned join the platoons with which they were riding. The captain, on dismounting, takes position at the point where he desires the base platoon to form or otherwise indicates that position to the leader of the base platoon. The platoon that was the base when the troop dismounted remains the base of the dismounted formation in the absence of other indication. Its leader takes position at once in rear of the captain, or as indicated by the latter, and the dismounted platoon forms in =double column= or as directed. The other platoons form so as to extend the formation =in line of double columns=, or as the captain orders, in accordance with the principles governing the assembly of the troop. The captain may direct the platoon leaders to proceed at once to designated positions without forming the troop as a unit. _In all cases the measures taken must be such as to prevent unnecessary exposure of men or horses to hostile view or fire._ DISMOUNTED COMBAT (THE TROOP). GENERAL CONSIDERATIONS. =650.= When the troop, acting alone, dismounts to engage in deliberate fire action the captain makes provisions for the led horses (par. 649) and at once sends out scouts (usually two experienced men detailed and trained as such) to the front to reconnoiter. The captain reconnoiters usually in rear of, but in touch with the scouts, and accompanied by platoon commanders and the first sergeant; he explains to them the purpose of the attack, gives them all the information he has about the enemy and about our own troops in the vicinity, points out to them the objective of each platoon if they are to advance, or indicates the part of the line to be held by each if to take the defensive.