Validation in several input file with JS

I have a JS code for validation of form attachments and I'm trying to call the function once for all fields with the same class="" The problem is that it only works with the first view the same field in the others views does not go through validation, it follows the codes.

valid-attachment.js // call function in include header.php

function verifica_extensao()
      {
      var arquivo = $(".input_anexo").val();

      var extensoes_permitidas = new Array(".jpg", ".jpeg", ".png", ".gif", ".pdf", ".php", ".js", ".swf", ".zip", ".rar", ".bmp", ".css", ".html", ".txt", ".doc", ".docx", ".word", ".7zip");
      var erro = "";
      if ($.trim(arquivo)=="")
      {
        return true;
      }
      else
      {
          var extensao = (arquivo.substring(arquivo.lastIndexOf("."))).toLowerCase();
          var permitida = false;
          for (var i = 0; i < extensoes_permitidas.length; i++) 
          {
            console.log("if ("+extensoes_permitidas[i]+" == "+extensao+") ");
            if (extensoes_permitidas[i] == extensao) 
            {
              permitida = true;
              break;
            }
          }
      }

      if (!permitida)
      {
        var ext_perm = "";
        for (a in extensoes_permitidas)
        {
          ext_perm += ext_perm == "" ? extensoes_permitidas[a] : " , " + extensoes_permitidas[a];
        }

        alert("Somente permitido envio de imagens com as seguintes extensoes: "+ext_perm);
        return false;
      }

      return true;
      }

This form is in two different views and works only in the first one.

new_quest.php // form to create new question

<?php echo form_open_multipart(current_url(), 'class="form-horizontal" onsubmit="return verifica_extensao()"'); ?>
        <div class="control-group">
          <label class="control-label">Área</label>
          <div class="controls">
            <select name="i_area" class="input-large">
            <option value="" selected="selected" disabled="disabled">Selecione uma Área</option>
            <?php 
                $query = $this->db->get('areas')->result_array();
                foreach ($query as $data) :
            ?>
                <option value="<?php echo $data['i_area']; ?>"><?php echo $data['nome']; ?></option>
            <?php 
                endforeach;
            ?>
            </select>
          </div>
        </div>
        <div class="control-group">
          <label class="control-label">Título</label>
          <div class="controls">
            <?php echo form_input('titulo', set_value('titulo'), 'class="input-xlarge" placeholder="Digite um Título"'); ?>
          </div>
        </div>
        <div class="control-group">
          <label class="control-label">Descrição</label>
          <div class="controls">
            <?php echo form_textarea('descricao', set_value('descricao'), 'class="input-xxlarge" rows="10" placeholder="Mensagem que será enviada e lida pelo técnico"'); ?>
          </div>
        </div>
      <div class="control-group">
          <label class="control-label">Arquivo</label>
          <div class="controls">
            <?php echo form_upload(array('name' => 'anexo_msg', 'class' => 'input_anexo')); ?>
          </div>
        </div>
        <div class="control-group">
          <div class="controls">
        <?php 
            echo validation_errors('<p class="text-error">', '</p>'); 
            if ($this->session->flashdata('msgok') != "")   echo '<p class="text-success">'.$this->session->flashdata('msgok').'</p>';
          if ($this->session->flashdata('msgerror') != "") echo $this->session->flashdata('msgerror');
        ?>
            <button type="submit" class="btn btn-primary">Enviar ao Suporte</button>
          </div>
        </div>
      <?php echo form_close(); ?>