Here is a screenshot.
On the left you can see the conversation in the message list. I have clicked on the message count for the conversation, and that has expanded the thread view.
On the right you can see the message preview. I have read the older message from you, so it and my reply is not displayed. It starts in the top of the preview pane exactly where I need to be to continue reading. If I want to see older messages in the conversation, I need to scroll up to display those behind the 2 older emails button.