atavistic coraco-brachialis-brevis (Testut), the epitrochleo-do 

 salis (Testut), and pectoralis tertius (Testut). 1 *. . 



Centers of Variability.— As the literature is so readily 

 accessible I will not multiply illustrations of the innumerable 

 congenital variations related to human evolution. I call 

 attention to several important inductions. First, there are 

 several centers in which both the skeletal and muscular 

 systems are highly variable. Second, that the most conspicu- 

 ous variations, and therefore the most frequently recorded, are 

 reversions. Third, that structure lags far behind function in 

 evolution. 



The conclusions of Wood and Testut 2 are that variability is 

 independent of age or sex, of general muscularity, and of 

 abnormal mental development. Wood found 981 anomalies 

 in 102 subjects ; of these, 623 were developed upon both sides 

 of the body, while 358 were unilateral. Of still greater interest 

 are the statistics collected by Wood between 1867-68 in the 

 dissecting-room of King's College, upon 36 subjects (18 of each 

 sex). These show that there are more anomalies in the limbs 

 than in the trunk ; that anomalies are rare in the pelvis ; that 

 there were 292 anomalies in the anterior limbs to 119 in the 

 posterior ; that in both limbs the anomalies increase toward 

 the distal segments, culminating in the muscles of the thumb, 

 where they rise to ninety per cent, (mainly flex. long, pollicis, 

 and abd. long, pollicis). These facts seem to prove conclusively 

 that while variation is universal it rises to a maximum in the 

 centers where human evolution is most rapid; here are 

 Herbert Spencer's conditions of unstable equilibrium. This 

 has a direct bearing, as I shall show, upon our theory of 

 heredity. 



Fortuitous Congenital Variations. — I have thus far con- 

 sidered only those variations which apparently have a definite 

 relation to the course of human evolution. There is an 



'Quain describes seventy anomalous muscles (Anat., Vol. I.) Testut describes a 

 still larger number. 



