MUSCLES 213 



arising under the stimuli of altered function, and only a few of 

 these will be dealt with. It might appear sufficient to those who 

 yield, perhaps too willingly, to authority, if I were here to try and 

 prove my point by quoting the statements of one of the greatest 

 anatomists of our time and country, and so pass on — but it is to be 

 feared authority cannot carry one far in a dispute so important. 

 Macalister says, however, " The anatomical arrangement of the 

 muscular system is the physical exponent of habitual actions and 

 those actions are the chief factors in moulding the bones and in 

 regulating the position of the somato -pleural vessels and nerves " — 

 and " the locomotory function and consequent utility of the trunk- 

 muscles were lost when the early vertebrates became terrestrial. 

 In higher vertebrates, and notably in man, the mobility of several 

 regions of the vertebral column differs both in degree and kind : 

 the outgrowing vertebrate processes show consequent variations, 

 and the muscular system is varied accordingly." 1 Also " as both 

 origins and insertions (of muscles) are the creatures of habit, they 

 are both equally variable with variation of function ; but, as in 

 higher animals the kind of work to be done is more constant than 

 its degree, so, as a rule, insertions alter less than origins." 2 

 Macalister, at any rate, held a very clear dynamical rather than 

 static view of the making of the muscular system. But as the 

 days of authority are in a certain sense gone for ever, and we live 

 under the reign of experiment, research and questioning, every 

 biologist, within certain limits, does what is right in his own eyes ; 

 there is no King in these days. 



Skeletal muscles are structures in which, if ever, the factors 

 of use and habit and disuse would be shown, because muscle is a 

 tissue, with highly active metabolism, so that it has been called 

 " an expensive tissue " for the animal to maintain. 



Muscles of Primates. 



This physiological fact agrees with the anatomical results of 

 an extended study in the musculature of primates, especially of 

 man, and Hartmann's book on Anthropoid Apes supplies abundant 

 evidence of the variations of the muscles of these animals, which 

 are not at all more striking than their differing modes of life would 

 suggest. It would be wearisome to quote all these, but a single 

 muscle may be given as an example of a special ape's muscle with 

 variable distribution. It is called latissimo-condyloideus and starts 

 from the insertion of the latissimus dorsi and passes along the inner 



1 Op. cit., p. 71. (Italics not in original.) 



2 Op. cit., p. 73. 



