THE MUSCLES OF THE FORE-LIMB 41 



be interpreted in two ways — the human condition may 

 be a new and gradual development from the stage seen 

 in the typical lower Eutherian Mammals, or it may be 

 a retention of an extremely primitive and generalized 

 vertebrate type of musculature. Most authorities upon 

 comparative anatomy appear to regard the ulnar head 

 of the M. pronator radii teres as a new development in 

 the Anthropoids — a development which becomes most 

 fully established and most fully perfected in Man. This 

 development is, by many, regarded as a reversion. This 

 point of view was taken by Gordon Taylor and Victor 

 Bonne}^, and they have concluded regarding this muscle : 

 " It may be objected that it appears rather strange that 

 in Man, a Mammal most highly specialized, and the most 

 highly evolved, the apparently older stage in evolution 

 of the muscle persists. But we must remember that in 

 him movement between the bones of the forearm has 

 reappeared in an extreme degree." Were the human 

 condition of this muscle to be an isolated phenomenon, 

 perhaps such an attitude might be justified; but when 

 the primitive type of every bone and joint of the human 

 fore-limb is taken into account, we must hesitate before 

 we name these things as " reappearances " in Man. 

 That the human ulnar head of the M. pronator radii teres 

 is a retention of a primitive type appears to me to be a 

 more reasonable view w^hen all the facts of the anatomy 

 of the fore-limb are taken into consideration. I therefore 

 regard this muscle of Man as being more akin to the 

 ancestral type than anything seen in the rest of the 

 living members of the Primates. 



As for the human M. pronator quadratus, it is usually 

 regarded as being only a partial survival of a primitively 

 extensive interosseous muscle, which is best developed 

 in quadrupedal forms. We have previously pointed out 

 that the interosseous muscle (M. radio-ulnaris) is on a 

 plane which is deep to that occupied by the true M. 

 pronator quadratus, and the nerve-supply points also to 



