Analyze optional tags in C #

I'm trying to find an easy and slick way to do the following requirement.

I have a XML message with this arrangement:

  <persons>
    <person>
       <firstName>Mike</firstName>
       <middleName>K.</middleName>
       <lastName>Kelly</lastName>
    </person>
    <person>
       <firstName>Steve</firstName>
       <lastName>David</lastName>
    </person>
    <person>
       <firstName>Laura</firstName>
       <middleName>X.</middleName>
       <lastName>Xavier</lastName>
    </person>
  </persons>

I want to parse this XML using xPath expressions.

persons/person/firstName
persons/person/middleName
persons/person/lastName

My objective is store firstName, middleName and lastName tag values like this into a list of string objects like this:

firstNameList[0] = "Mike";
firstNameList[1] = "Steve";
firstNameList[2] = "Laura";

middleNameList[0] = "K.";
middleNameList[1] = null;
middleNameList[2] = "X.";

lastNameList[0] = "Kelly";
lastNameList[1] = "David";
lastNameList[2] = "Xavier";

In my C# code, I do this:

XmlNodeList firstNameNodeList = xmlDoc.SelectNodes("persons/person/firstName", nsmgr);
XmlNodeList middleNameNodeList = xmlDoc.SelectNodes("persons/person/middleName", nsmgr);
XmlNodeList lastNameNodeList = xmlDoc.SelectNodes("persons/person/lastName", nsmgr);

The problem with this code is that for middle name, I don't have it for 2nd person in my XML list. So the middleNameNodeList returns 2 values (K. and X.) but I wouldn't know whether the 1st or 2nd or 3rd person's middle name is missing.

I was hoping that SelectNodes() API would provide an iteration or index ID as which repeating element has a given value.

Please suggest me an easiest way to achieve what I needed? Thanks so much for your help, JK

How about this?

foreach (Node person in xmlDoc.SelectNodes("persons/person", nsmgr))
{
    firstNameNodeList.Add(person.SelectSingleNode("firstName", nsmgr));
    middleNameNodeList.Add(person.SelectSingleNode("middleName", nsmgr));
    lastNameNodeList.Add(person.SelectSingleNode("lastName", nsmgr));
}