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Because the Fontainemelon caliber 97 is a center seconds design and uses a directly driven design, the layout of the wheels varies from the classic wheel train.  As illustrated, the center wheel (1 ) lies at the bottom of the train, in the center of the movement.  The center wheel drives the third wheel (2) pinion.  The third wheel drives the fourth wheel (3) pinion.  And the third wheel drives the escape wheel (4).

The fourth wheel, as in all watch movements, makes one full rotation each minute. A movement that has a "directly driven" center seconds, has a seconds hand driven directly by the fourth wheel.  (Indirect center seconds usually drives the seconds hand off of the third wheel with appropriate reduction to rotate the seconds hand once per minute.)  The unusual layout of the FM-97 allows the fourth wheel to remain in the center of the movement.  The long pinion of the fourth wheel ( below left, red arrow) extends through the hollow pinion of the center wheel (2, below right) and carries the seconds hands.  The illustration below right also shows the center wheel itself (1 ) and the mainspring barrel (3).
 

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