NATURAL SELECTION 



391 



tern 



stm 



Fig. 205. — Skulls of (A) the sabre-tooth tiger, Smilodon, and (B) a cat, Felv^, 

 showing contrasting skull form and musculature, c, occipital condyle; 

 cl. VI., cleidomastoid; dig., digastric; m, mastoid process; mas, masseter; 

 si. m., sternomastoid; /em., temporalis. (From Lull, after Matthew.) 



acters, the extreme of variation opposite to any useful character 

 is hkely to be a hindrance, and is certain to operate in direct 

 competition to determine the loser. 



