452 THE EVOLUTION OF LIFE. 



been of like size with those borne by other kinds of deer ; 

 and if we suppose that in certain individuals, they became 

 larger by spontaneous variation ; what would be the con- 

 comitant changes required to render their greater size useful ? 

 Other things equal, the blow given by a larger horn would 

 be a blow given by a heavier mass moving at a smaller 

 velocity : the momentum would be the same as before ; and 

 the area of contact with the body struck being somewhat 

 increased, while the velocity was decreased, the injury done 

 would be less. That the horns may become better weapons, 

 the whole apparatus which moves them must be so strength- 

 ened as to impress more force on them, and to bear the more 

 violent reactions of the blows given. The bones of the skull 

 on which the horns are seated must be thickened ; otherwise 

 they will break. To render the thickening of these bones 

 advantageous, the vertebrae of the neck must be further de- 

 veloped ; and without the ligaments that hold together these 

 vertebrae, and the muscles which move them, are also enlarged^ 

 nothing will be gained. Such modifications of the neck will 

 be useless, or rather will be detrimental if its fulcrum be not 

 made capable of resisting intenser strains : the upper dorsal 

 vertebrae and their spines must be strengthened, that they 

 may withstand the more violent contractions of the neck- 

 muscles ; and like changes must be made on the scapular 

 arch. Still more must there be required a simultaneous de- 

 velopment of the bones and muscles of the fore-legs ; since 

 each of these extra growths in the horns, in the skull, in the 

 neck, in the shoulders, adds to the burden which the fore- 

 legs have to bear ; unless this deer with its heavier horns, 

 head, neck, and shoulders, had stronger fore-legs, it would 

 not only suffer from loss of speed but would even fail in fight. 

 Hence, to make larger horns of use, additional sizes must be 

 acquired by numerous bones, muscles, and ligaments, as well 

 as by the blood-vessels and nerves, on which their actions 

 depend. On calling to mind how the spraining of a single 

 small muscle in the foot, incapacitates for walking, or how a 



