#main_nav {
		background: url(../images/nav_end.jpg) no-repeat top right;
		clear: both;
		height: 55px;
		margin: 0;
		padding: 0;
		}
		
			#main_nav a {
			float: left;
			height: 55px;
			margin: 0;
			padding: 0;
			text-decoration: none;
			}
			
			#main_nav a span {
			display: none;
			}
			
			#main_nav a:hover {
			background-position: 0 -55px;
			}
			
			a.nav_departments {
			background: url(../images/nav_departments.jpg) no-repeat;
			width: 106px;
			}
			
			a.nav_centers {
			background: url(../images/nav_centers.jpg) no-repeat;
			width: 159px;
			}
			
			a.nav_programs {
			background: url(../images/nav_programs.jpg) no-repeat;
			width: 240px;
			}
			
			a.nav_library {
			background: url(../images/nav_library.jpg) no-repeat;
			width: 193px;
			}