It might have struck the reader that the story of the bear impaled on the North Pole had no connection with the problem that followed. 
As a matter of fact it is essential to a solution. 
Eleven bears cannot possibly be arranged to form of themselves seven rows of bears with four bears in every row. 
But it is a different matter when Captain Longbow informs us that "they had so placed themselves that there were" seven rows of four bears. 
For if they were grouped as shown in the diagram, so that three of the bears, as indicated, were in line with the North Pole, that impaled animal would complete the seventh row of four, which cannot be obtained in any other way. 
It obviously does not affect the problem whether this seventh row is a hundred miles long or a hundred feet, so long as they were really in a straight line—a point that might perhaps be settled by the captain's pocket compass.