The Saints tied up a shock deal for the 21-year-old Uruguayan winger on deadline day for an undisclosed sum, believed to be in the region of £12 million.
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"It underlines the ambition of the club that we've been able to attract such a talented young individual like Gaston," Adkins told the club's official website.
"He's got a massive future in the game, so we're delighted. He's already talked about the project and the vision that has been set out by the chairman, Nicola Cortese.
"Everything that we're doing here is very positive at Southampton and this signing underlines the progressive nature that we've got."
Ramirez stated that he was excited to begin a new chapter in his career, and was pleased to be able to play in the England.
"I know that just a few years ago the club was in the third division, so they have had a great increase in success to be in the Premier League now," he said.
"I have been following the Premier League since before I was in Italy - that was a positive experience, but now I am delighted to be here in England and to play in the Barclays Premier League.
"The stadium is great and I had a very positive impression from the manager. I also know the people here and the supporters are very warm, so I'm just looking forward to beginning my experience here.
"Now, I am sure I can do very well for the club and contribute to our success."