128 S. R. DETWILER 
ment into the definitive limb bud which centers ventral to the 
fourth myotome. Such convergence having taken place, a typi- 
cal normal plexus as illustrated in figure 2 would be produced. 
It has long since been pointed out, expecially by Fiirbringer 
(79), that the nerve plexus from which a limb is supplied might, 
in two cases, have a different segmental origin and yet the in- 
trinsic nerves arising from the plexus might be distributed in 
the same manner in each. 
From his own transplantation experiments, Harrison (’07) 
showed that there are two main factors involved in the develop- 
ment of the innervation of a limb: first, the position and extent 
Fig. 2 Graphic reconstruction of the normal left brachial plexus of case AS4o.5 
(fig. 13), preserved sixty-eight days after the operation. XX 20. mn.sp.cor., nerve 
to musc. supracoracoideus; n.p.cor., nerve to musc. procoracohumeralis; 7.d.sc., 
nerve to muse. dorsalis scapulae; n.pc., nerve to muse. pectoralis; n.sb.sc., nerve 
to muse. subcoraco scapularis; n.cor.br., nerve to musc. coraco-brachialis; 
n.lt.dor., nerve to muse. latissimus dorsi. 
of the extremity at the time of origin which determines the 
source of the nerve supply, and, secondly, the mode of segre- 
gation and growth of the individual structures of the limb which 
governs the intrinsic distribution of its nerves. 
As the result of a study of the normal plexus formation, in 
addition to the observations of Harrison, the evidence at hand 
tends to show that the position and extent of the limb rudiment 
serves as an index of the number of spinal nerves supplying the 
extremity, the number corresponding with that of the segments 
occupied by the limb rudiment at the period when initial con- 
nection is made. This, then, would not only readily account 
