зверек,
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
<script>
window.onload = function() {
var a = document.querySelector("em:first-of-type"),
b = document.querySelector("em:last-of-type"),
next_em = a.nextSibling,
c = [a.tagName];
while(next_em) {
c.push(next_em.tagName||next_em.nodeName);
if(next_em == b) break;
next_em = next_em.nextSibling;
}
alert(c.join("\n"))
};
</script>
</head>
<body>
<em>
знач.1
</em>
<br>
<em>знач.2 </em>
<em>
<br>
знач.3
</em>
<br>
<em>знач.4</em>
</body>
</html>