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  The Leinster back-rower has been out for a number of weeks with a calf injury but has taken a full part in training since Tuesday.
  Iain Henderson starts in the second row as Donnacha Ryan has been struggling this week with a knee injury.
  Ian Keatley is named as fly-half Paddy Jackson's understudy on the bench, which also includes winger Tommy Bowe.
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  Ryan has been suffering from a niggling medial ligament injury and has not trained since Tuesday.
  "We wanted a bit more certainty about him but at the same time Iain has done a super job for us in the past," explained Ireland coach Joe Schmidt at the team announcement.
  Keith Earls and Simon Zebo start on the wings.
  Regular number 10 Johnny Sexton was ruled out of the Murrayfield match earlier this week as the calf injury he picked up in Leinster's Champions Cup game against Castres on 20 January has not yet fully healed.
  The 31-year-old has an "outside chance" of being fit to face Italy in Rome on 11 February, according to Schmidt.
  Sexton's unavailability leaves Ulster's Jackson to make his sixth start in eight games for Ireland, his last coming in the victory over Australia in Ireland's final autumn international in November.
  Munster flanker Peter O'Mahony is out with a hamstring problem so open-side O'Brien joins blind-side flanker CJ Stander and number eight Jamie Heaslip in the back row.
  Andrew Trimble's absence with a groin injury left Earls and Zebo as obvious choices to join full-back Rob Kearney in the back three, with Bowe getting the nod among the replacements ahead of Craig Gilroy or Tiernan O'Halloran.
  Garry Ringrose and Robbie Henshaw form the midfield pairing, with Conor Murray joining Jackson to make up the half-back partnership.
  Up front, the front row combination of Jack McGrath, Rory Best and Tadhg Furlong is retained, while Devin Toner joins Henderson at lock.
  Uncapped hooker Niall Scannell and his Munster front-row partner John Ryan are listed as replacements in preference to James Tracy and Finlay Bealham.
  BBC Scotland's Tom English
  Ireland's team is formidable, despite Johnny Sexton not being in it. It's an illustration of their depth that Donnacha Ryan, a standout in the second-row in the victory over New Zealand, can't now get into the 23.
  Jared Payne and Jordi Murphy, two more heroes from that historic victory, are long-term injuries, but Ireland are still loaded with class, power and experience.
  Ireland: R Kearney; K Earls, G Ringrose, R Henshaw, S Zebo; P Jackson, C Murray; J McGrath, R Best, T Furlong; I Henderson, D Toner; CJ Stander, S O'Brien, J Heaslip.
  Replacements: N Scannell, C Healy, U Dillane, J Ryan, J van der Flier, K Marmion, I Keatley, T Bowe.
target: Flanker Sean O'Brien has been named in the Ireland team to face Scotland in Saturday's Six Nations opener.