112 THOMPSON YATES LABORATORIES REPORT 
with one surface of the more proximal part of the limb (forearm, leg). Each also supplies with 
motor and afferent fibres, a complete band of muscular tissue extending throughout the whole 
length of the limb from the attached base to the free apex. Of each the proximal part of the 
sensory distribution is buried in the deep tissues, and nowhere reaches the cutaneous surface, 
whereas the distal part is distributed in the sensory nerves of the cutaneous as well as of the deep 
parts. 
Striking, too, is the likeness existing between the distribution of the Ilnd thoracic nerve 
and the Vlllth post-thoracic nerve as regards the limb. Each of these nerves supplies the 
muscles at the apex of the limb [e.g.., the intrinsic muscles of hand and of foot). Each supplies 
also an analogous area of the skin, widely sundered from its muscular field, namely, an area of 
skin on the posterior face of the proximal portion of the limb (/.c, the axillary extensor aspect of 
the upper arm as far down as a point close below the elbow ; the skin over the flexor group of the 
thigh muscles to just below the knee). 
To my mind, any attempt to trace out homologies between the brachial and pelvic limbs 
must pay regard to the remarkable resemblances between the contributions given by the above 
pairs of segmental nerves. For this reason I cannot subscribe to the antitropic scheme of 
homology recently revived by Eisler,* and worked out by him with such ingenuity and labour. 
In Eisler's scheme of homology the Vlllth cervical segment is the homologue of the Ilird 
lumbar (of Man ; the fourth post-thoracic of Macacus) ; the Ilnd thoracic segment is then made 
to correspond with the 1st lumbar (of Man). I cannot but insist that the analogy — and, in my 
opinion, nothing more than analogy has as yet been available, or at least employed, in instituting 
comparison between the limbs — between Vlllth cervical and Vth lumbar (of Man ; Vlth lumbar 
of Macacu%\ and between the Ilnd thoracic and the Ilnd sacral is infinitely greater than between 
any of the segments that are coupled together as homologous in Eisler's elaborate, careful, but 
to my mind untenable scheme ot comparison. 
My observations are, I consider, altogether adverse to any antitropic scheme ; they are 
more compatible with a syntropia of the limbs. The composition of the anterior part of the 
brachial limb certainly resembles that of the anterior part of the pelvic limb more than it 
resembles the posterior part of that latter, in segmental structure both of muscles and skin. This 
greater resemblance is evident both in the number and step-like arrangement of segments, and in 
the mutual relation obtaining in each segment between the position of its muscular and its 
cutaneous portions. 
I must here, however, to avoid misapprehension, repeat my previously-expressed conviction, 
that it is altogether idle to look for exact homologies between the component parts of the brachial 
and pelvic limbs. ' The ontogeny of the brachial limb is distinct from that of the pelvic limb. The 
correspondence between the two is similarity not identity. A general^ but not a particular^ resemblance is 
to be expected between the segmental components of the two^\ and that is all that has been found. 
More instructive than to attempt to construe identity out of approximate resemblance is to note 
* 'Homologie der Extremit'aten,' Halle, 1895. 
t Sherrington, ' Lumbo-sacral Plexus.' 'Joiirn. of Physiol.,' vol. 13, 1892. 
