6oo SCIENCE PROGRESS 



hip-flexors contract semitendinosus, although a potential extensor 

 of hip, contracts. It is used as a knee-flexor and knee-flexion 

 often accompanies hip-flexion. But semimembranosus, which lies 

 alongside oi semitendinosiis, never contracts with the hip-flexion; 

 it relaxes : it is a hip-extensor and a true antagonist of the 

 hip-flexors and is always used as such ; it is used as if it had 

 no influence at knee. Pseud-antagonists are a numerous class ; 

 they fixate a joint in order that double-joint muscles crossing 

 it may act better at another joint. True antagonism is dealt 

 with by " reciprocal innervation " ; pseud-antagonism by 

 " identical innervation." 



4. Reflex Inhibition and Transition from One Muscular 

 Act to Another 



Not only does inhibition play a part in the co-ordination of 

 muscles in simultaneous co-operation at one and the same 

 moment of time ; it also plays its part in the co-ordination of 

 successive steps in a reflex series. One muscular act follows 

 another and the same musculature is commonly employed for 

 different effects in succession. The execution of the change 

 from the old muscular act to the new is ushered in by an 

 inhibitory suppression of the discharge of motor centres pre- 

 vailing previously (figs. 6, 7) as well as by a discharge of motor 

 centres previously at rest. Take the case where a reflex 

 (decerebrate) preparation is exhibiting the steady postural reflex 

 of standing and then draws up one foot on that foot being 

 pinched. The extensors of the leg are in contraction as the 

 animal stands; if then one foot be squeezed the foot is lifted 

 and drawn up out of harm's way. In this action not only are 

 the flexors of knee, hip and ankle thrown into contraction by 

 the new reflex, but the extensors of knee and hip and ankle 

 which were engaged in contraction by the previous reflex of 

 standing are thrown out of action and their motor centres 

 brought to rest by inhibition. In the transition from one 

 reflex to another a muscle's activity is inhibited if it would 

 offer obstruction to the new reflex. Inhibition ushers in the 

 new reflex by wiping out any antagonistic persistence of the 

 old. In default of this inhibition one of two things must 

 happen : either, the stimulus which is exciting the old reflex 

 must cease exactly as the stimulus exciting the new one begins 



