Wales boss Wayne Pivac has handed Ospreys flanker Jac Morgan a Test debut in Saturday's Guinness Six Nations clash against Scotland, as both sides ring the changes.

Scotland flanker Jamie Ritchie has been ruled out for the rest of the Six Nations with a hamstring injury.

The 25-year-old went off in the second half of last weekend's victory over England, and the Scottish Rugby Union confirmed, while announcing the team to face Wales in Cardiff on Saturday, that his campaign is over.

Morgan, 22, replaces Ellis Jenkins in one of four Welsh changes and lines up at openside flanker in a reshaped back-row that also sees Ross Moriarty start at number eight instead of Aaron Wainwright, with Taine Basham wearing the number six shirt.

Elsewhere, Morgan's Ospreys colleague - wing Alex Cuthbert - makes a first Six Nations appearance for five years, being preferred to Johnny McNicholl.

But Cuthbert's fellow wing Josh Adams, who started at outside centre in last Saturday's Six Nations opener against Ireland in Dublin that Wales lost 29-7, is ruled out because of a tight calf muscle, so Owen Watkin fills the number 13 position.

Pivac has resisted any temptation to make further changes, while captain Dan Biggar makes his 100th Test match appearance for Wales and the British and Irish Lions, becoming the ninth Welshman to achieve that feat.

Biggar wins a 97th Wales cap, with Wainwright among the replacements, but McNicholl and Jenkins, who skippered Wales in Autumn Nations Series games against Fiji and Australia this season, drop out completely.

Scotland have not won in Cardiff for 20 years, losing eight Six Nations Tests, a World Cup warm-up game and an autumn international during that time.

But they will arrive at the Principality Stadium following a stirring Calcutta Cup victory over England last weekend that confirmed serious Six Nations title credentials.

Wales, meanwhile, have not started a Six Nations campaign with successive defeats since 2007, and they must beat Scotland to revive any hope of a successful title defence.

In one of five changes to the Scotland side that started the Calcutta Cup match, Ritchie will be replaced by Exeter's Sam Skinner for this weekend's trip to the Principality Stadium.

There are three changes to Gregor Townsend's front row for the match in Cardiff, with Edinburgh's Pierre Schoeman and WP Nel starting alongside hooker Stuart McInally.

Glasgow's Sione Tuipulotu comes in to make his third Scotland appearance at inside centre.

Zander Fagerson, George Turner and Rory Sutherland drop to the bench, while Sam Johnson has been released to play for Glasgow on Friday.

Edinburgh's Grant Gilchrist will win his 50th cap at lock.

Glasgow flanker Rory Darge is among the substitutes and will win his first cap if he gets off the bench. Scrum-half Ben White, who scored a debut try against England last weekend, is again a replacement, alongside Blair Kinghorn and Cam Redpath.

Wales: Liam Williams; Alex Cuthbert, Owen Watkin, Nick Tompkins, Louis Rees-Zammit; Dan Biggar, Tomos Williams; Wyn Jones, Ryan Elias, Tomas Francis, Will Rowlands, Adam Beard, Taine Basham, Jac Morgan, Ross Moriarty.

Replacements: Dewi Lake, Gareth Thomas, Dillon Lewis, Seb Davies, Aaron Wainwright, Gareth Davies, Callum Sheedy, Jonathan Davies.

Scotland: Stuart Hogg; Darcy Graham, Chris Harris, Sione Tuipulotu, Duhan van der Merwe; Finn Russell, Ali Price; Pierre Schoeman, Stuart McInally, WP Nel, Jonny Gray, Grant Gilchrist, Sam Skinner, Hamish Watson, Matt Fagerson.

Replacements: George Turner, Rory Sutherland, Zander Fagerson, Magnus Bradbury, Rory Darge, Ben White, Blair Kinghorn, Cameron Redpath.

Watch Wales v Scotland live on RTÉ2 and RTÉ Player this Saturday from 1.30pm. Follow all of Ireland's Six Nations games via our live blogs on and on the RTÉ News App or listen to live radio coverage on RTÉ Radio 1. Watch live TV coverage of England v Ireland (12 March, 4.45pm) on RTÉ2 and the RTÉ Player. Highlights on Against the Head, RTÉ2, Mondays, 8pm.