62 EVOLUTION 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 ve/iguza. It seems highly probable that a 
