EW1 12 valve SOHC ??

I'm new to these engines and don't understand the full function of the 4th valve in this head.
Initially I thought it was an Aux. intake valve but notice that it is next
to the exhaust valve.
My Chilton manual doesn't provide any help..
May seem like a dumb question but it's got me stumped. Once I have an understanding of this question, I'm sure I'm going to have a few more before I get this nice little car ('85 CRX) running properly.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.