ion's head
The Lion's head is a variation for the cautious player. Because black castles the King is in a safe position. Of course a pawn's attack with the g- and h-pawn is less of an option. In the book this is the variation with the most branches. That's because it's a complicated variation with many options. Especially strategic players will find this a useful variation. 
Because of the many possibilities it is difficult to define a main-line. The first 6 moves are basic moves. After that there are many option. Below I'll describe a very agressive variation. Whichever course you follow it is best to try and reach the following position after 15 moves. 
Ideale stelling voor zwart Black is mostly active on his own side of the board. The only pieces that could cross the border are Be7-b4 or Nf6-g4. Square f4 becomes very important for black, it is the ideal square for a black Knight. Square f5 continues to be a weak square for black, which has to be guarded by the Bishop. 
1.  e2-e4     d7-d6    
2.  d2-d4   Ng8-f6    
3.  Nb1-c3  Nb8-d7    
4.  Ng1-f3   e7-e5    
5. Bf1-c4  Bf8-e7    
6. 0-0        0-0  The base moves have been played. 
7. Qd1-e2  e5xd4 White can also continue here with Re1, h3 or Be3. In all cases black has to work towards the ideal position. White's Qd1-e2 clears the way for setting the d-line by Rooks. This move makes the sham sacrifice of Nxe4 impossible and puts pressure at f7 if its followed by Bb3 and Qc4. Black can also continue with c6.  
8. Nf3xd4, Nd7-e5 With Nxd4 black attacks the powerful white Bishop. Also this moves makes the sham sacrifice at e4 possible again because d5 is being guarded by the black Queen. 
9. Bc4-b3  c7-c5 White is forced to move his Bishop. Black's c7-c5 weakens square d5 and pawn d6 but keeps the initiative on black's side.   
10. Nd4-f5  Bc8xf5 The white Knight can't be left at f5. Black has to exchange Bishops. 
11. e4xf5  Qd8-d7 Black now has an extra pawn in the centre, while white is stuck with a double pawn. Black of course has a weak d5 and d6.   
12. Nc3-d5  Rf8-e8 White defends his pawn at f5. When black exchanges, a Bishop at d5 follows, which also attacks the pawn at b7. It is better to guard the Bishop. 
13. Rf1-d1  Be7-d8 White guards his Knight and square d5.   
14. Nd5-e3  Bd8-c7 Black can also play Nc6. This leads to wild positions.  
15. c2-c3    Re8-e7 Black doubles his Rooks and has a clear advantage. White has to give up pawn f5. Also the centre falls in the hands of the black Knights and pawns. 
This variation of the Lion can clearly lead to wild games. It seems the Lion really doesn't have any cautious variations. 
Here follows a nice game by Fabiano against Kosten, who also played a Lion's head. 
Fabiano- Kosten, 1991; 0-1