Antagonistic Muscles and Reciprocal Innervation, 185 



previous posture of flexion, which is again as before steadily main- 

 tained. 



Conversely, when, as not unfrequently occurs in conditions of 

 narcosis resembling that above referred to, the arm has assumed a 

 posture of extension, and this is tonic and maintained, the oppor- 

 tunity is taken to excite the appropriate focus in the cortex, pre- 

 viously ascertained, for flexion of forearm or upper arm. Triceps 

 is then found to relax, and the biceps at the same time enters into 

 active contraction. If the biceps be hindered from actually moving 

 the arm, the prominence at the back of the upper arm due to the 

 contracted triceps is seen simply to sink down and become flattened. 

 When examined by palpation the muscle is felt to become more or 

 less suddenly soft, and the biceps at the same time to become tenser 

 than before. The movement of the limb, when allowed to proceed 

 unhindered, is flexion with some supination. It is noteworthy that 

 in this experiment not every part of the large triceps mass becomes 

 relaxed; a part of the muscle which extends from humerus to the 

 scapula does not in this experiment relax with the rest of the muscle. 

 This part, if the scapula be fixed, acts as a retractor of the upper 

 arm, and is not necessarily an antagonist of the flexors of the elbow. 

 This part of the triceps we observed sometimes enter active contrac- 

 tion at the same time as the flexors of the elbow. It should be 

 remarked that under use of currents of moderate intensity we find 

 that not from one and the same spot in the cortex can relaxation and 

 contraction of a given muscle be evoked at differenc times, but that 

 the two effects are to be found at different, sometimes widely sepa- 

 rate, points of the cortex, and are there found regularly. 



We have obtained analogous results in the muscles acting at the 

 hip-joint. When in the narcotised animal the hip-joint is being 

 maintained in flexion, the thighs being drawn up on the trunk, 

 excitation of the region of the cortex previously ascertained when 

 the limbs hang slack to evoke extension of the hip, produces relaxa- 

 tion of the flexors of the hip and at the same time active contraction 

 of the extensors of the thigh. We examined particularly the 

 psoas-iliacus, and the tensor fasciae femoris, also the short and long 

 adductor muscles. Each of these was found to relax under appro- 

 priate cortical excitation. If the knee were held by the observer it 

 was found at the time of relaxation of the flexors of the hip to be 

 forced downward by active extension of the hip. 



Similarly with other groups of antagonistic muscles both those of 

 the small apical joints of the limb, e.g., flexors and extensors of the 

 digits, and those of the large proximal joints, e.g., adductors and 

 abductors of the shoulder. At these also instances of reciprocal 

 innervation were obtained. 



That a part of the triceps brachii (that retracting the upper arm) 



VOL. lxii. p 



