That is, the first Received line is your own system or mail server. Received line is where the mail originated. Each mail system has its own style of Received line. A Received line typically identifies the machine that received the mail and the machine that the mail was received from. The id is for logging purposes and may help system admins track the unwanted email message if you can get them to cooperate.
Many mailers add extra information.
In this case, the mailer inserted the IP address of the sending system. If the machine name does not match the IP address, you have likely identified the point where the mail was injected. Any Received lines that follow are likely to be forgeries. Contact a system admin for more advice in determining if an IP address has been forged. If the entire Received line is fake, then the injection point is somewhere above in the headers.