Where's the SA Node?

Just heard this story today.One houseman is not happy that he was being extended in Orthopedic posting.Medical MO: "Why did it happen?"HO: "This is totally unreasonable. They were asking me something unrelated to orthopedics and they failed me just because I answered wrongly!"MO: "Oh that's bad. What did they ask you?"HO: "They asked me where the SA (sinoatrial) node is!"MO: "Oh...that's like