How can I display an image description, from an image gallery?

I have a vanilla install of WordPress 3.6. I’m using the Twenty Thirteen theme. I’ve created some galleries. On the individual image page, the “caption” is displayed below the image. I’d like to display the images “description” instead. How can I do that?

Link to example image page: http://1dayranch.jasonormand.com/dogs/winston/

Here is the image.php file code

<div id="primary" class="content-area">
    <div id="content" class="site-content" role="main">
        <article id="post-<?php the_ID(); ?>" <?php post_class( 'image-attachment' ); ?>>
            <header class="entry-header">
                <h1 class="entry-title"><?php the_title(); ?></h1>

                <div class="entry-meta">
                    <?php
                        $published_text = __( '<span class="attachment-meta">Published on <time class="entry-date" datetime="%1$s">%2$s</time> in <a href="%3$s" title="Return to %4$s" rel="gallery">%5$s</a></span>', 'twentythirteen' );
                        $post_title = get_the_title( $post->post_parent );
                        if ( empty( $post_title ) || 0 == $post->post_parent )
                            $published_text = '<span class="attachment-meta"><time class="entry-date" datetime="%1$s">%2$s</time></span>';

                        printf( $published_text,
                            esc_attr( get_the_date( 'c' ) ),
                            esc_html( get_the_date() ),
                            esc_url( get_permalink( $post->post_parent ) ),
                            esc_attr( strip_tags( $post_title ) ),
                            $post_title
                        );

                        $metadata = wp_get_attachment_metadata();
                        printf( '<span class="attachment-meta full-size-link"><a href="%1$s" title="%2$s">%3$s (%4$s &times; %5$s)</a></span>',
                            esc_url( wp_get_attachment_url() ),
                            esc_attr__( 'Link to full-size image', 'twentythirteen' ),
                            __( 'Full resolution', 'twentythirteen' ),
                            $metadata['width'],
                            $metadata['height']
                        );

                        edit_post_link( __( 'Edit', 'twentythirteen' ), '<span class="edit-link">', '</span>' );
                    ?>
                </div><!-- .entry-meta -->
            </header><!-- .entry-header -->

            <div class="entry-content">
                <nav id="image-navigation" class="navigation image-navigation" role="navigation">
                    <span class="nav-previous"><?php previous_image_link( false, __( '<span class="meta-nav">&larr;</span> Previous', 'twentythirteen' ) ); ?></span>
                    <span class="nav-next"><?php next_image_link( false, __( 'Next <span class="meta-nav">&rarr;</span>', 'twentythirteen' ) ); ?></span>
                </nav><!-- #image-navigation -->

                <div class="entry-attachment">
                    <div class="attachment">
                        <?php twentythirteen_the_attached_image(); ?>

                        <?php if ( has_excerpt() ) : ?>
                        <div class="entry-caption">
                            <?php the_excerpt(); ?>
                        </div>
                        <?php endif; ?>

                    </div><!-- .attachment -->
                </div><!-- .entry-attachment -->

                <?php if ( ! empty( $post->post_content ) ) : ?>
                <div class="entry-description">
                    <?php the_content(); ?>
                    <?php wp_link_pages( array( 'before' => '<div class="page-links">' . __( 'Pages:', 'twentythirteen' ), 'after' => '</div>' ) ); ?>
                </div><!-- .entry-description -->
                <?php endif; ?>

            </div><!-- .entry-content -->
        </article><!-- #post -->

        <?php comments_template(); ?>

    </div><!-- #content -->
</div><!-- #primary -->