(Devarim, Ibid. 22) "And of Dan he said": Why is this written? Because it is written (Bereshith 47:2) "And from the 'edge' of his brothers he (Joseph) took five men and presented them to Pharaoh," here it is specified that he took them from those whose names were doubled, and Dan was one of them.
"Dan is a lion's whelp": We are hereby taught that Dan was close to the border, and all who are close to the border are compared to lions (see Ibid. 20).
"he shall leap forth from the Bashan": Just as "leaping forth" (zinuk) connotes leaving one place and being divided into two, so the tribe of Dan took its portion in two places, viz. (Joshua 19:47) "And the boundary of the children of Dan went forth from them, and the sons of Dan went up and they battled, etc."