From the report summary: "The Senate meets in the Senate chamber of the Capitol. Seated at the head of the chamber on the top of a two-tiered dais is the presiding officer. Members are assigned to the 100 desks that are arranged in a semicircle facing the presiding officer. The center aisle in the Senate chamber divides the political parties. Facing the presiding officer, Republicans sit to the right of the center aisle, Democrats to the left. Senior Members usually sit the closest to the dais and along the center aisle, although some choose other desks. The party floor leaders occupy the front aisle desks, which may also be used by Senators who are managing floor consideration of a bill or nomination. Seated around the presiding officer are various officers and employees of the Senate who have defined roles, some of which are prescribed in Senate rules and others of which are derived from precedent."
CRS Report for Congress, 98-397