On Reciprocal Liner vation of Antagonistic Muscles. 415 



to the muscles of antagonistic position acting about certain joints of 

 the limbs. 



If transection of the neural axis be carried out at the level of the 

 crura cerebri in, e.g., the cat, there usually ensues after a somewhat 

 variable interval of time a tonic rigidity in certain groups of skeletal 

 muscles, especially in those of the dorsal aspect of the neck and tail 

 and of the extensor surfaces of the limbs. The details of this condi- 

 tion, although of some interest, it is unnecessary fco describe here and 

 now, except in so far as the extensors of the elbow and the knee are 

 concerned. These latter affect the present subject. The extensors of 

 the elbow and the knee are generally in strong contraction, but alto- 

 gether without tremor and with no marked relaxations or exacerba- 

 tions. On taking hold of the limbs and attempting to forcibly flex 

 the elbow or knee a very considerable degree indeed of resistance is 

 experienced, the triceps brachii and quadriceps extensor cruris 

 become, under the stretch which the more or less effectual flexion puts 

 upon them, still tenser than before, and on releasing the limb the 

 joints spring back forthwith to their previous attitude of full exten- 

 sion. Despite, however, this powerful extensor rigidity, flexion of 

 the elbow may be at once obtained with perfect facility by simply 

 stimulating the toes or pad of the fore foot. When this is done the 

 triceps enters into relaxation and the biceps passes into contraction. 

 If, when the reflex is evolved, the condition of the triceps muscle is 

 carefully examined, its contraction is found to undergo inhibition, and 

 its tenseness to be broken down synchronously with and indeed very 

 often accurately at the very moment of onset of reflex contraction in 

 the opponent prebrachial muscles. The guidance of the flexion 

 movement of the forearm may therefore be likened to that used in 

 driving a pair of horses under harness. The reaction can be initiated 

 in more ways than one, electrical excitation of a digital nerve or 

 mechanical excitation of the sensory root of any of the upper cervical 

 nerves may be employed ; I have seen on one occasion a rubbing of 

 the skin of the cheek of the same side effective. 



Similarly in the case of the hind limb. The extensor muscles of 

 the knee exhibit strong steady Don-tremulent contraction under the 

 appropriate conditions of experiment. Passive flexion of the knee 

 can only be performed with use of very considerable force, the quad- 

 riceps becoming tight as a stretched string. The application of hot 

 water to the hind foot then elicits, nevertheless, an immediate flexion 

 at knee and hip, during which not only are the flexors of those joints 

 thrown into contraction, but the extensors of the knee joint are 

 simultaneously relaxed. Electric excitation of a digital nerve or of 

 the internal saphenous nerve anywhere along its course will also 

 initiate the reflex. 



The same relaxation of existing contraction in the extensors can 



