Of all Jack's poses, this one is by far my favorite. We call it the GQ. He typically uses this move mid-crawl when he is distracted by something (usually a toy, Cheerio or electrical cord) and has to stop to check it out. If he decides that the item in question is worth investigating, he will then pull himself up to a sitting position. He isn't technically crawling, since he hasn't coordinated his arm & leg movements yet, but he can sure get around. Over the last few days he has gotten very fast - we spend most of the day chasing him down. I don't think that is going to change anytime soon :)
Please excuse the mess behind him. He really likes to get all his toys out & scatter them all over the room. Is he too young to learn the "Clean Up Game"?!?