ii6 
THOMPSON YATES LABORATORIES REPORT 
The details of the composition of the musculature of the fore-limb of Macacus by these six 
rays are given in the accompanying tabular statement. The fore-limb of the Monkey, just as its 
hind-limb, proves when examined by the analysis of spinal root distribution, to be a lateral fin 
with a sloping anterior and an abrupt posterior border, and this fin is built up of six rays. 
With regard to Herringham's generalizations* regarding the scheme of innervation of 
the musculature of the limb, my observations are in complete harmony with his rule, that : ' Of 
two muscles, or of two parts of a muscle, that nearer the head end of the body tends to be 
supplied by the higher, that nearer the tail end by the lower nerve.' This is so : almost as a 
matter of course if the limb, as the theory asserts, is built up of lateral extensions of the segmental 
series of the body. And if, as I urge, the members of this segmental series, when taken from 
before backward, jut further and further from the median plane of the trunk, there follows as a 
corollary from the first rule that second rule which Herringham lays down, namely, that the 
musculature of the apex of the limb belongs to segments posterior to some of those in the attached 
base of the limb. Here it is that the curious fact comes in — that the most posterior segment 
which contributes to the limb musculature contributes in each limb to the extreme apex and to the 
extreme base, but not to the upper arm (or thigh), so that the hindermost muscular ray is one with 
a break in its middle portion. 
Herringham's third rule runs : ' Of two muscles, that which is nearer the surface tends 
to be supplied by the higher, that which is further from it by the lower nerve.' 
With this my results on the lower limb did not agree ; and I look upon my observations 
on the upper as confirming in this particular those upon the lower extremity. Herringham's 
conception of the musculature of the limb is, I take it, that of a central core derived from lower 
segments overlaid by a peripheral sheet derived from higher. The conception to which my own 
observations lead me is of a simpler kind — -a series of fused, partially commingled, segmental 
muscular strata, placed one upon another in such a way that, to transfix them in true antero- 
posterior series, one would in the upper arm enter the front of the deltoid and emerge at the inner 
head of the triceps, or in the forearm pass obliquely from the extensors of the wrist near the radial 
border and out through the flexors near their ulnar border. The muscles on the extensor aspect 
of the wrist tend to be supplied by roots segmentally anterior to those which supply the muscles 
of the flexor aspect ; and those near the radial border by roots segmentally anterior to those 
supplying muscles near the ulnar border. Hence the flexor profundus digitorum is segmentally 
posterior to the extensor communis digitorum, not because the former is deeper than the latter, 
but because the flexor aspect of the hand is posterior to the extensor aspect. I find the palmaris 
longus, superficial muscle as it is, and lying in the proximal region of the forearm as it does, is one 
of the most posterior muscles of the whole limb in segmental position ; the flexor sublimis 
digitorum lias in several observations seemed to me to contract more vigorously than the flexor 
profundus on excitation of the 1st thoracic, less vigorously than the flexor profundus on excitation 
of the Vllth cervical root. The fact that so deep-lying a muscle as the pronator quadratus gets 
' Pioc. Roy. Soc.,' vol. 41, p. 441, 1S87. 
