Matthew McConaughey and girlfriend Camila Alves reveal their newborn baby boy Levi Alves McConaughey in OK! magazine ... and the actor says the couple got "tribal" during his birth.

"We found a great rhythm," says McConaughey, 38. "Contractions started kicking in. I sat there with her, right between her legs. We got tribal on it, we danced to it! I was DJ-ing this Brazilian music."

Levi was born at Santa Monica-UCLA Medical Center and weighed 7 lbs., 4 oz.

Click here to see Levi and to read more in OK!

"I have it all chronicled," McConaughey told OK! "Becoming a dad is something I've dreamed of doing since I was 10. Becoming a father felt very, very natural. We were jamming! She was sweating. No painkiller, let's go. She just clicked into that gear that only a woman has at a time like this. We'd been up for 40-something hours, and we went from dead tired to a really steadfast, 'Let's handle this … let's stay in the rhythm. Don't let the contraction be more than you.'"

Ultimately, Alves underwent a C-section.

"He came out with the umbilical cord wrapped around his neck, so it was the right thing to do," McConaughey tells the magazine. "Of course, if we’d known this was how it was going to go, we could have gotten it done in the first three hours. We laughed, but that was Mother Nature and the baby saying, 'Thank goodness for Western medicine.'"