PHESEXT IM;nliJj;.MS IX I'.VOLirrioN AND H Kl.-KDll'V. 3'-J7 



related to liuiiuiii (nolutioii. I call attention to se\cral iinptjirant in- 

 ductions. First, there are several centers in which l)otli the skeletal 

 and ninscrilar systems are hijihly variable, f^econd, that the most con- 

 si)icuons variations, and therefore the most fre([nently iccoided. are 

 leversions. Third, that structure lags far behind function in e\ oliition. 

 The conclusions of Wood, antl of Testut,* are that vaiiabilit.\- is inde 

 Iteudent of age or sex, of general muscularity, and of abnormal mental 

 develoi)ment. Wood found 981 anomalies in 102 subjects: of these, 023 

 were developed upon both sides of the body, while o.lS were unilateral. 

 Of still greater interest are the statistics collected by Wood between 

 1807-'(JS in the dissecting room of Iving's College, u])on Mi 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 ])osterior; 

 that in both lind)s the anomalies increase toward the distal segments, 

 culminating in the muscles of the thund), where they rise to 90 jmh- 

 cent, (mainly tlexor longus pollicis, and abductor longus pollicis). 

 These facts seem to prove conclusively that while Aariation is universal 

 it rises to a maximum in the centers where human evolution is most 

 rapid; here are Herbert S])encer's conditions of unstable erpiilibrium, 

 This has a direct bearing, as 1 slmll show, upon our theory of her<'dity. 



Fortuitous roiifiniildl raridtioiis. — 1 have thus far considei'ed only 

 those variations which ai>parently have a definite relation to the course 

 of human evolution. Ther<' is an entirely different class of congenital 

 variations which ma\' be desciibed as fortuitous or indefinite l)ecause 

 they do not occur in any lixed ]»ercentage of cases; they are liable to 

 take any direction; they can not b<' considered reversional because 

 rhey are not found in the hyi)othetical atavus, and there is not sufH- 

 cient evidence to cause us to c<»nsi(ler them as inci)>icnt features of our 

 future structure. 



Sonu^ ini'.y not be truly congenital (/. c. si)iinging direct fiom the 

 germ cells) but may be merely deviations from the norinal course of 

 development. I may instance the variations in the carpus recorded by 

 Turnerf in which the tiapezium and sca])hoid unite, or the trapezoid 

 and semilunar di\ide, or tlu^ astragalus and navicular unite (Ander- 

 son). 



The best example of fortuitous congenital variations are seen in su- 

 ])ernumeraiy tingers and vertebra'. The eighth cer\ical \etebra, beai- 

 ing a ludinientary rib,i is not a reversion because the most remote aii- 

 cestois (»f mail have but seven cervicals. In cases whcie a rib is de- 

 xcloped upon the seventh cervical, however, the reveision theory is 

 perhaps applicable because rib bearing cervicals are relatively less re- 



'' Sur les Anomatien Mii><ciiltih(s, )>. TfiO. 



\,lniiin<(l of Aiialomji and I'ln/Kiolof/n, 1881, ]>. I'lf). 



jArli. Lane: Journal <>/ Anotonui and rhi/.iiolo(/i/. issr>, |i. 2tll>. 



