120 THE STRUCTURE OF MAN 
development of the superficial muscles of the posterior surface 
of the fore-leg, ve. of the calf. The gastrocnemius and soleus 
were formerly as directly connected with the sole of the foot or 
with its fascia as was the plantaris. The terminal tendons of 
these muscles have alike shifted back to the calcaneal tuberosity ; 
but while the plantaris very soon began to degenerate, the soleus 
and gastrocnemius! have attained an excessive development speci- — 
fically characteristic of Man. We have here another instance of 
retrogressive and progressive changes taking place side by side 
in one and the same region.” 
RETROSPECT 
Gathering together the conclusions which follow from the 
above review of the musculature, we find first that age seems to 
have no influence on the frequency of variation ‘and reversionary 
phenomena. We must, however, except foetal life, since, during 
that period, certain muscles may appear which afterwards suffer 
more or less complete degeneration. 
No definite laws can be framed either as to the disposition 
or division, the symmetry or asyinmetry, of the muscles, or as 
to the general condition of the body to which they belong, e.g. 
the strength or weakness of the individual. Correlative changes 
counteracting those due to variation are not observed. It is the 
exception to find that anomalies extend to the homologous 
muscles of the fore- and hind-limbs of the same side. 
Examination of eighteen male and eighteen female bodies by 
Professor Wood at King’s College, London (in 1867-68), led to the 
conclusion that anomalies are more frequent in the musculature of 
the limbs than in that of the rest of the body, and that the fore- 
hmb is in particular distinguished by their occurrence (292 varia- 
tions were found in the fore as against 119 in the hind-limb). 
It has further been ascertained that variations become more 
frequent as examination proceeds in a distal direction, 7.e. as those 
peripheral parts of the body are reached which are more directly 
exposed to the modifying influences of the environment. 
1 A sesamoid bone sometimes occurs near the lateral point of origin of the 
gastrocnemius. In Anthropoids and many other Mammals several such bones 
(fabellee) are found, one, for instance, at the median point of origin of the muscle. 
2 Various circumstances point to the fact that the biceps femoris, semitendinosus | 
and semimembranosus, originally arose higher up than at present, viz. from the 
ilium, and the sacral, or caudal vertebre. The fact that they have wandered on to 
the ischial tuberosity would appear to be connected with the forward translocation 
of the pelvic girdle already discussed (ante, p. 33). 
