Get URL ID Code and insert into JS

When you have a URL of this type:

http://URL/galerias.php?galeria=casais

the ?galeria=casais part is called query string and you can fetch it with window.location.search " in string format. Now you just need to remove that info, for example via regex. If the key value you are looking for is galeria you can do this:

$(document).ready(function() {
    var query = window.location.search;
    var match = window.location.search.match(/galeria=(\w+)/);
    var galeria = match && match[1];
    $('#conteudo').load('galeria.php?galeria=' + prodId, 
      function(){
        $('#gallery a').lightBox();
      }
    );
});

The reason I first do match and then galeria = match && match[1]; is because in case there is no match avoid giving access error match[1] , because if there is match method will give null and not array .

You can recover by php

$galeria = $_GET['galeria'];

Then create an input of type hidden in html

<input type="hidden" id="galeria" value="<?php echo $galeria; ?>">

and finally retrieve it in javascript

var proId = $('#galeria').val();

It's a way I thought at first, I think there might be something better.

obs: I did not get to test

Dude, the way you're doing all this seems pretty complicated, why do not you try to simplify?

To know which gallery was selected you could do something like this:

<ol>
    <li class="galeria" data-galeria="casais">Casais</li>
    <li class="galeria" data-galeria="gravidas">Gr&aacute;vidas</li>
    <li class="galeria" data-galeria="criancas">Crian&ccedil;as</li>
    <li class="galeria" data-galeria="bebes">Beb&ecirc;s</li>
</ol>

And to load the galleries that are being clicked you do the following:

$(document).on("click", ".galeria", function()
{
    var galeriaSelecionada = $(this).data("galeria");

    $('#conteudo').load('galeria.php?galeria=' + galeriaSelecionada, 
      function(){
        $('#gallery a').lightBox();
      }
    );
});