Set innerHTML of Span in Modal

I'm trying to open a modal and then set the innerHTML of a span, but can't seem to get it working.

The modal is

        Modal::begin([
            //'header'=>'<h4>Add a New Company</h4>',
            //'headerOptions' => ['id' => 'modalHeader'],
            'id'=>'modalPopup',
            'class'=>'modalPopup',
            'size'=>'modal-lg',
            'header' => '<span id="modalHeaderTitle"></span>',
            'headerOptions' => ['id' => 'modalHeader'],
            'closeButton' => [
                'label'=>'Close',
                'id'=>'closeButton',
                'class'=>'btn btn-warning pull-right',
            ],
            'clientOptions' => [
                'backdrop' => 'static', //true,
                'keyboard' => false, // true,
            ]
        ]);
        echo '  <div id="modal-system-messages" style="opacity: 1; display: none"></div>';
        echo "<div id='modalContent'></div>";
        Modal::end();

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And then my js for the calling button is

$(function(){
    $('.showModal').click(
        function (){
            //Open the modal window
			$('#modalPopup').modal('show')
				.find('#modalContent')
				.load($(this).attr('value'));
			// Set the modal title span
			// alert($(this).attr('title'));
			$('#modalPopup #modalHeader #modalHeaderTitle').innerhtml = '<h4>' + $(this).attr('title') + '</h4>';
        }
    );
});

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I have validated that alert($(this).attr('title')); is returning the proper value but the .innerHTML line does nothing.

Thank you for your help.