308 



The Intrinsic Factors in the Act of Progression in the Mammal. 

 By T. Graham Brown. 



(Communicated by Prof. C. S. Sherrington, F.B.S. Eeceived July 21, 1911.) 

 (From the Physiological Laboratory of the University of Liverpool.) 

 CONTENTS. 



PAGE 



I. Introduction 308 



II. Operative Procedure 312 



III. Movements of Progression in the Low Spinal Preparation in which 



the Muscles are not De-afferented 313 



IV. Movements of Progression in the Low Spinal Preparation in which 



the Muscles are De-afferented 314 



V. Conclusions 316 



VI. Summary 319 



I. Introduction. 



Whilst the act of progression is being performed, the several limbs 

 exhibit rhythmic movements of flexion and of extension. When any limb 

 is in contact with the ground, it extends, and thus serves to propel the 

 animal forwards. At the end of this act the limb is lifted from the ground 

 by a movement of flexion, is carried forward, and finally is again placed 

 upon the ground to repeat the cycle. During these phasic acts the dynamic 

 balance of the neural centres is disturbed by two different kinds of peripheral 

 stimuli. 



In the first place, the discontinuous contact with the ground, and the 

 synchronous distortion of the skin of the foot — determined by the weight of 

 the animal then carried in part by that limb — produce changes in the 

 activity of exteroceptive end-organs therein embedded, and discontinuous 

 augmentations and diminutions of the stimuli originated in them. 



In the second place, the backward and forward movements of the limb, 

 and the activity of the muscles which execute them, produce changes in the 

 state of the proprioceptive organs situated in the muscles, joints, and 

 tendons which take part in the act. 



The act of progression is one richly co-ordinated. Yet it has long been 

 known that movements of the hind limbs, certainly those of progression, 

 may be present in the " late spinal animal. 1 ' A mechanism confined to the 

 lumbar part of the spinal cord is therefoi*e sufficient to determine in the 

 hind limbs an act of progression, which is probably very nearly a normal 

 one. As reflex movements of the hind limb, exactly similar to movements 



