Yossi Benayoun had put the Gunners ahead in the second minute but Wes Hoolahan’s effort trickled past Wojciech Szczesny to level the score, before Grant Holt’s shot took a wicked deflection off Kieran Gibbs to hand the visitors the lead.
Robin van Persie’s double after the break edged Wenger’s men ahead for the first time in the game, but Morison’s 85th-minute strike pulled the Canaries level in a frantic finish.
The result leaves Arsenal just two points ahead of Tottenham and Newcastle, who both play their games in hand on Sunday, leaving the Gunners’ hopes of a top-four finish hanging in the balance.
“We were [too frail defensively], of course,” said Wenger after the game. “We lost too many challenges and it is surprising because recently we were quite good, but today I feel that defensively the whole team was very poor.
“It is more than frustrating because we were very poor in the first half, not switched on.
“The quality of our first half was absolutely not at the level we wanted in a decisive game like that.
“In the second half we did very well. We created at least 10 chances but again not only did we not take our chances, but on top of that we gave them a third goal in a situation that was absolutely unbelievable.
“In the end we got punished for our mistakes.”
Meanwhile, Norwich boss Paul Lambert was full of praise for his side’s battling display in north London.
“We kept going and kept going and got what we deserved,” he said. “Robin van Persie is one of the best players in the world and you know if you give him a chance he will take it.
“But I thought some of our blocks in the second half were terrific and John Ruddy was at the top of his game.”
He added: “The last three years have been a fairytale story for us. The players have been the ones that have galvanised the club – they deserve all the plaudits.”
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