PRESENT rR(^]5LEMS IX I^'OLUTION AND HEREDITY. 32o 



rrtMiiiciit i)r:u'ti('e aiiiouii- .Vmericaii (Iciitists of relieviiii;' the crow (led 

 Jaw by extraction. 



We now turn to the arches and limbs, b'lower has pointed out that 

 The base of tiic scapuhi is widenin*;- in the hij:j,lier races, so that the 

 •'index," or ratio of length to breadth, is quite distinctive, (lejienbaur 

 associates tliis witli the development of the scapulo-luuneral muscles 

 and tiie greater play of the humerus as a prehensile organ. 



In general, the arm increases in interest as we descend towaid the 

 hand, both in the skeleton and musculature, because here we meet with 

 tlie lirst glimpses of facts which enable us to form some estimate of the 

 rate of human evolution. The well-known humeral toi-sion (connected 

 with increased rotation) ascends from 1.">LJ^ in the polished stone age to 

 1(54'^ in the modern European. The intercondylar foramen, or ]»ertbra- 

 tion of the olecranon fossa, is exceptionally well recorded;* it is found 

 in.'U) i»ercent of skeletons of the reindeer period; in the (h)lmen period 

 it fell to 24 per cent: in Parisian cemeteries between the fourth and 

 tenth centuries it is found in ~>.r} per cent; it has now fallen to ."{..j [)er 

 cent. The condylar foramen, occasionally forming a complete bridge 

 of bone above the inner condyle and transmitting the median nerve 

 and brachial artery, is known as the "entepicondylar" foramen in com- 

 parati\(' anatomy, and is one of the most ancient (diaracters of the 

 mammalia; it reveits paheogenetically in 1 per cent of lecent skeletons, 

 but mu(di more fre(iuently in inferior races (Lamb). In the wrist bone 

 is sometimes developed another extremely old structure — the oscentrale. 

 (Irubert reported its recurrence at 0.25 per cent ap])roximately. This 

 is a case of neogenetic reversion, for Lebouc(]:j: shows that there is a 

 distinct (icntrale in every human carpus in the first ])art of the second 

 month, which iH)rmally fuses with the scaphoid l)y the middle of the 

 tidrd month. 



The divergence of the fennile from th(^ male ])elvis is an important 

 fcatuic of our ])rogressi\'e de\"eloi>inent; it is proved by the fact tliat, 

 as w(> descend among the lower races it l)e(!omcs increasingly difticult 

 to distinguisli the female s]<(>leton from tlie male, for the pelves of the 

 two sexes are nearly uniform. Here it seems to me is a most interest 

 ing problem for investigation. Arbuthnot Lane's§ views oflhe nu-chan- 

 ical causers of this divergence, whicth are strongly Lamarckian. may be 

 weighed with the theory of survival of the fittest, for the large femah' 

 pelvis is perha[ts the In^st <'xample that can be adduced of a skeletal 

 variation which would be i)i-esei\-ed l»y natural selection, foi- reasons 

 which are self-cnident. The third trochanter of the femur is believed 

 by Prof. Dwight,|| of the Harvard Medical School, to be a true re- 



* See Blanchard, op. fit., p. ir»(). 



t VircLow's Archir,, 188.5, p. 353. 



t Ann. (h; la Soc. dv Med. dr (iaud, J.S'Sf. 



^ Joiinnil III' Aiiatomi/ (iiid /'hi/siologi/, ISSS. p. L>1 1. 



]\Ihid., 1S!)(), p. 61. 



