120 THE STKUCTUEE OF MAX 



development of the superficial muscles of the posterior surface 

 of the fore-leg, i.e. 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 l 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. 2 



EETROSPECT 



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 fcetal 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 asymmetry, 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- 

 limb 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, i.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 

 (fabellfe) 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 vertebrae. The fact that they have wandered on to 

 the ischial tuberosity would appear to be connected with the forward tianslocation 

 of the pelvic girdle already discussed (ante, p. 33). 



