Change individual markers in google maps direction

I have an issue with adding individual markers in Google maps API. I searched a lot like the following link, Change individual markers in google maps directions api V3 . But I am unable to implement the same on my code. With the help of suppressMarkers: true I am able to prevent the default markers. Now only root directions are showing. Now how can I add the makers for start point and end point. Following is my code.

   function GoogleMap_selected(){

        var lattitude_value= document.getElementById('slectedLat').value;
        var longitude_value= document.getElementById('slectedLon').value;

        var from = new google.maps.LatLng(mylatitude, mylongitude);
        var to = new google.maps.LatLng(lattitude_value, longitude_value);

         var directionsService = new google.maps.DirectionsService();
         var directionsRequest = {
           origin: from,
           destination: to,
           travelMode: google.maps.DirectionsTravelMode.DRIVING,
           unitSystem: google.maps.UnitSystem.METRIC
         };

        this.initialize = function(){
        var map = showMap_selected();

         directionsService.route(
                  directionsRequest,
                  function(response, status)
                  {

                    if (status == google.maps.DirectionsStatus.OK)
                    {
                      new google.maps.DirectionsRenderer({
                        map: map,
                        directions: response,
                        suppressMarkers: true

                      });
                    }
                    else
                        {
                         alert("Unable to retrive route");
                        }
                var leg = response.routes[ 0 ].legs[ 0 ];
                makeMarker( leg.start_location, icons.start, "title" );
                makeMarker( leg.end_location, icons.end, 'title' );
                  }
                );

        }

function makeMarker( position, icon, title ) {
 new google.maps.Marker({
  position: position,
  map: map,
  icon: icon,
  title: title
 });
}

 var icons = {
  start: new google.maps.MarkerImage(
   // URL
   'start.png',
   // (width,height)
   new google.maps.Size( 44, 32 ),
   // The origin point (x,y)
   new google.maps.Point( 0, 0 ),
   // The anchor point (x,y)
   new google.maps.Point( 22, 32 )
  ),
  end: new google.maps.MarkerImage(
   // URL
   'end.png',
   // (width,height)
   new google.maps.Size( 44, 32 ),
   // The origin point (x,y)
   new google.maps.Point( 0, 0 ),
   // The anchor point (x,y)
   new google.maps.Point( 22, 32 )
  )
 };


         var showMap_selected = function(){
            var mapOptions = {
            zoom: 12,
            center: new google.maps.LatLng(lattitude_value, longitude_value),
            mapTypeId: google.maps.MapTypeId.ROADMAP
            };
            var map = new google.maps.Map(document.getElementById("selected_map_canvas"), mapOptions);
            return map;
        }
        }

Can anyone suggest me that how to implement adding of markers at both start and end points with respect to my code.

Changes:

pass the map variable into the makeMarker function (as DrMolle observed)
change icon URLs to ones that work on my server
move the code that adds the markers so it only runs if the route request succeeds

working fiddle

function GoogleMap_selected() {

    var lattitude_value = document.getElementById('slectedLat').value;
    var longitude_value = document.getElementById('slectedLon').value;

    var from = new google.maps.LatLng(mylatitude, mylongitude);
    var to = new google.maps.LatLng(lattitude_value, longitude_value);

    var directionsService = new google.maps.DirectionsService();
    var directionsRequest = {
        origin: from,
        destination: to,
        travelMode: google.maps.DirectionsTravelMode.DRIVING,
        unitSystem: google.maps.UnitSystem.METRIC
    };

    this.initialize = function () {
        var map = showMap_selected();

        directionsService.route(
        directionsRequest,

        function (response, status) {

            if (status == google.maps.DirectionsStatus.OK) {
                new google.maps.DirectionsRenderer({
                    map: map,
                    directions: response,
                    suppressMarkers: true
                });
                var leg = response.routes[0].legs[0];
                makeMarker(leg.start_location, icons.start, "title", map);
                makeMarker(leg.end_location, icons.end, 'title', map);

            } else {
                alert("Unable to retrive route");
            }

        });

    }

    function makeMarker(position, icon, title, map) {
        new google.maps.Marker({
            position: position,
            map: map,
            icon: icon,
            title: title
        });
    }

    var icons = {
        start: new google.maps.MarkerImage(
        // URL
        'http://maps.google.com/mapfiles/ms/micons/blue.png',
        // (width,height)
        new google.maps.Size(44, 32),
        // The origin point (x,y)
        new google.maps.Point(0, 0),
        // The anchor point (x,y)
        new google.maps.Point(22, 32)),
        end: new google.maps.MarkerImage(
        // URL
        'http://maps.google.com/mapfiles/ms/micons/green.png',
        // (width,height)
        new google.maps.Size(44, 32),
        // The origin point (x,y)
        new google.maps.Point(0, 0),
        // The anchor point (x,y)
        new google.maps.Point(22, 32))
    };


    var showMap_selected = function () {
        var mapOptions = {
            zoom: 12,
            center: new google.maps.LatLng(lattitude_value, longitude_value),
            mapTypeId: google.maps.MapTypeId.ROADMAP
        };
        var map = new google.maps.Map(document.getElementById("selected_map_canvas"), mapOptions);
        return map;
    };
}

code snippet:

// 32.715738, -117.1610838
// 40.7127837, -74.0059413
var mylatitude = 40.7127837;
var mylongitude = -74.0059413;

function GoogleMap_selected() {

  var lattitude_value = document.getElementById('slectedLat').value;
  var longitude_value = document.getElementById('slectedLon').value;

  var from = new google.maps.LatLng(mylatitude, mylongitude);
  var to = new google.maps.LatLng(lattitude_value, longitude_value);

  var directionsService = new google.maps.DirectionsService();
  var directionsRequest = {
    origin: from,
    destination: to,
    travelMode: google.maps.DirectionsTravelMode.DRIVING,
    unitSystem: google.maps.UnitSystem.METRIC
  };

  this.initialize = function() {
    var map = showMap_selected();

    directionsService.route(
      directionsRequest,

      function(response, status) {

        if (status == google.maps.DirectionsStatus.OK) {
          new google.maps.DirectionsRenderer({
            map: map,
            directions: response,
            suppressMarkers: true
          });
          var leg = response.routes[0].legs[0];
          makeMarker(leg.start_location, icons.start, "title", map);
          makeMarker(leg.end_location, icons.end, 'title', map);

        } else {
          alert("Unable to retrive route");
        }

      });

  }

  function makeMarker(position, icon, title, map) {
    new google.maps.Marker({
      position: position,
      map: map,
      icon: icon,
      title: title
    });
  }

  var icons = {
    start: new google.maps.MarkerImage(
      // URL
      'http://maps.google.com/mapfiles/ms/micons/blue.png',
      // (width,height)
      new google.maps.Size(44, 32),
      // The origin point (x,y)
      new google.maps.Point(0, 0),
      // The anchor point (x,y)
      new google.maps.Point(22, 32)),
    end: new google.maps.MarkerImage(
      // URL
      'http://maps.google.com/mapfiles/ms/micons/green.png',
      // (width,height)
      new google.maps.Size(44, 32),
      // The origin point (x,y)
      new google.maps.Point(0, 0),
      // The anchor point (x,y)
      new google.maps.Point(22, 32))
  };


  var showMap_selected = function() {
    var mapOptions = {
      zoom: 12,
      center: new google.maps.LatLng(lattitude_value, longitude_value),
      mapTypeId: google.maps.MapTypeId.ROADMAP
    };
    var map = new google.maps.Map(document.getElementById("selected_map_canvas"), mapOptions);
    return map;
  };
}

function initialize() {
  var instance = new GoogleMap_selected();
  instance.initialize();
}

google.maps.event.addDomListener(window, 'load', initialize);

html,
body,
#selected_map_canvas {
  height: 100%;
  margin: 0px;
  padding: 0px
}

<script src="https://maps.googleapis.com/maps/api/js?v=3&libraries=geometry"></script>
<div id="panel">
  <input type="text" id="slectedLat" value="32.715738"></input>
  <input type="text" id="slectedLon" value="-117.1610838"></input>
</div>
<div id="selected_map_canvas"></div>
<div id="directions-panel"></div>