INTEGRATION OF MOVEMENTS IN LEARNING IN THE RAT 411 



moved. The hind limb thrusts, when the tail is dorsally extended, 

 are directed downward and backward. 



The exact nature of these reflex extensor thrusts must be stud- 

 ied in their harmonious cooperation with other reflexes and their 

 importance in the behavior of rats for all integrated reflexes are 

 coordinated. In whatever position the head of a well developed 

 rat is passively moved, reflex extension of some limbs and reflex 

 flexion of others occurs, with contraction and relaxation of the 

 trunk and back muscles. If the head of the rat is passively bent 

 to the right of the midline of the body, then to the left of this 

 line, extension and flexion of all limbs takes place in the manner 

 of rhythmic progression. The direction of these thrusts is toward 

 the side in which the head is bent. These extensions and flex- 

 ions of the limbs reveal conditions for progression to one side, 

 or around an object and not directly ahead. These thrusts in 

 addition to revealing posture with the head turned to one side, 

 as Sherrington maintains, reveal the manner of progression in 

 the direction in which the head is turned. Furthermore the reflex 

 thrusts evoked when the head is dorsally extended to 45 degrees 

 of the midline of the body, show not alone, as Sherrington again 

 states, a modification of reflex standing posture, the animal as- 

 suming a posture in the act of looking up at an object with the 

 fore limbs extended and the hind flexed, but also in the act of 

 jumping, or moving an object upward with the muzzle. The 

 same thing is true of the condition of the limbs when the tail is 

 dorsally extended or when the head is bent ventralward. This 

 position of the body is not exclusively for looking under objects, 

 but also for moving low objects about with the muzzle and for 

 progression under objects. In decerebrate forms, only one con- 

 dition is revealed a modification of the reflex standing position; 

 in the living animals a modification of progression as well is 

 noted, such as jumping, crawling under objects, and moving 

 objects about with the muzzle. In many cases there results 

 not only a modification of a standing upright position, but also 

 progression in an upright position. When objects are raised 

 upward by the muzzle of an animal, there exists either a modifi- 

 cation of the reflex standing position or a modification of an up- 



