PRESENT PIK^BLEMS IN EVOI.IJTIOX AND IIEREDITV. ,'V2r) 



TIk' variations in tlic imisciilar system mark oti' more clearly the 

 re.uioiis of contemporary evolution, and therefore are even moreinstruc- 

 ti\e than those in the skeleton. Muscular anomalies have however 

 nev«-r been adeijuately analyzed. IWvw the remarkable memoir of M- 

 'I'estut, •' Sur les Anomalies miisculaires," is defective in not clearly 

 distiuijuishinn- between variations whii'h look to the future, those which 

 revei't to the past, and those whicli are fortuitous, foi- the authiu- is 

 stroufily inclined t;> refer all anomalies lo revei'sion. 



The law of muscular evolution is specialization by the successive 

 separation of new independent contractih^ bands from tlu^ lai,u-c funda 

 mental nuiscles, while the law of skeletal evolution is re(bicti(ni <tf 

 ])rimitive parts and the s])ecializatiou of articular surfaces. The num- 

 ber of mus<'les ill the itrimates as ;! whole has therefore been steadily 

 increasinj^-, while the number of bones has been dimimishinii'. In man 

 the number of nuiscles is ])robably increasinii- in the i-e^ions of the 

 lower arm. and diminishiuii' in every other reuion. Tiie analysis is 

 rendered very dihicult by the fact that some muscles {e. </., those con- 

 nei'tinn- the shonhh'r with tlie neck and back) rev<'rt to a formm- condi- 

 tion of greater specialization when they were employed in swin.uin^- the 

 body by the arms, and in (pia(lrui)edal locomotion; while (►ther nuiscles 

 {(■. //., those connectin^y- the lV)rearm and tini;ers) revert to a former 

 simpler arranj^'cment when the hand was mainly a liraspin;;- or.i:an, and 

 the thumb was not o])i)osable. 



As in the skeh^ton, we fuul that muscular anomalies include (I) 

 l)ala'Oi4'enetic reversions, or complete restorations of lost muscles; {2) 

 neoiicnetic r<'versions, oi' revivals of former tyi)es in the relatior.s of 

 existin;;- muscles; (.")) proj^ressive variations, which either by deueiuM-- 

 ation or specialization point to future types; (4) fortuitous variations, 

 which cannot be referred to either of the above. 



Duval observes that the tlexor lonjius policis re])eatsin reversion all 

 ihc sla.ues of its evolution between man and the a.})es, in which it is a 

 dixision of the tlexor ])rofundus. (Jruber and others lia\'e escji obser\-ed 

 the absiMice of the thumb ten(h)n. This is true of all the new nuiscles. 

 Of this Testut writes: 



•• Ne (lirait-on ])as, <'n le voyant sYdoigiuM- si souventde son ('tat nor- 

 mal. <pu' la nature Noudraitle remeuer a sa dis])osition ])rimiiive, lut- 

 tant ainsi sans cesse contre I'adaptation, et ne lui abandonimnt, (pT a 

 i'e<ii'et Tune (leases ]>lus belles conquetes.'' 



Speaking' of the hand, Uaker says: 



''On comi)arin;.': the human hand with that oftlu^ anthropoids, it may 

 be seen that this efliciem-y is produced in two ways — iirst increasint;' 

 the mobility and variety of action of the thumb and linu'crs; second, 

 reducing' the nuiscles nsed mainly to assist ])rolon<;'ed .urasp, the\' be 

 inu nil lonti'cr necessar\' to an oru'aii Ibi' dclicati' \\(n'k' reipiirin^' cori- 

 stant r<'-a(ljustment.*''* 



••Till' Ascent uI'MmM." I'nxrnliiKI^ itn. /.x.vor. Iilr. ,SV;. ]S!)(t, vol. \ \ X I V , ].. ISrK?. 

 Also, Sniilh-souiiiii h'ljiorl. ISHO, p. 111). 



