You can use blocks. In your index.volt :
<html>
<body>
{% block page_header %}{% endblock %}
{% block page_body %}{% endblock %}
{% block page_footer %}{% endblock %}
</body>
</html>
Then, in edit.volt for example:
{% extends 'index.volt' %}
{% block page_header %}
Page header
{% endblock %}
{% block page_body %}
Page content
{% endblock %}
{% block page_footer %}
Page footer
{% endblock %}