62 E VOL UTION AND DISEASE. 



will therefore come within the range of natural selec- 

 tion." 



In connection with these remarks it will be well to 

 note the very small amount of utility which will deter- 

 mine the persistence of an organ ; take, for instance, the 

 hind limbs of the python and viper which are only 

 of occasional use, in connection with procreative function, 

 yet this is sufficient to preserve them whilst all other 

 traces of limbs have long disappeared. Mammals 

 abound in instances of muscles which in some species 

 are large and important, whilst in others they may sub- 

 serve such trivial functions that when absent they are not 

 missed from a utilitarian standpoint, yet even this trivial 

 amount of service ensures their preservation. This is 

 well illustrated by the small muscle underlying the 

 clavicle of man, known as the subclavius. In birds 

 it is large and powerful, raising the wing in the act of 

 flying. In man it is small, insignificant, and steadies the 

 clavicle during movement of the arm. It has been found 

 as a band of fibrous tissue, and in a few cases absent. 



In reference to supposed useless parts, Wallace is of 

 opinion that the assertion of inutility in the case of any 

 organ or peculiarity which is not a rudiment or a cor- 

 relation, is not, and never can be, the statement of a fact 

 but merely an expression of our ignorance of its purpose 

 or origin. In the above quotation the term rudiment 

 refers to such parts as the pineal body, the vermiform 

 appendix, and teeth which are developed but rarely cut 

 the gum. These are vestiges of organs probably of great 

 importance to the ancestors of the forms in which they 

 now persist as reliquia. It seems highly probable that a 



