What is difference between HttpResponseMessage.Headers and HttpResponseMessage.Content.Headers

I'm trying to integrate my service with third-party service. The service returns me a file with Content-Type and Content-Disposition headers. I expected the headers will be returned in HttpResponseMessage.Headers, but I got'em in HttpResponseMessage.Content.Headers Why are some type of headers could be returned in HttpResponseMessage.Headers and some other types in HttpResponseMessage.Content.Headers?