INTEGRATION OF MOVEMENTS IN LEARNING IN THE RAT 407 



tractions of the fore limbs are inhibited, the fore quarters are 

 lowered and those of the hind quarters raised. This last effect 

 is also obtained when the tail is dor sally raised. Modifications 

 obtained by bending the head and neck to the right, producing 

 increased extensor tone in the left fore limb is similar to what 

 normally occurs when the animal in standing posture, gazes to 

 the right; the reverse is the case when the head is bent to the left, 

 extensor tone of the right limb increases when gazing to the left. 

 From these investigations, particularly those of Sherrington, 

 some of the reflexes revealed may be said to be used when the 

 rat solves the latch-box problem. Additional observations with 

 other rats substantiated this view. The neck movement to 

 raise the latch is accompanied by increase extensor tone of the 

 fore, and flexion of the hind limbs as had previously been ob- 

 served. For when this movement occurs in rats, the fore limbs 

 are seen to be extended and the hind flexed, and this reflex pos- 

 ture is identical with that obtained from a decerebrate cat when 

 the head is raised dorsally. Concerning any integration of these 

 reflexes with the trunk muscles nothing has been said; but Sher- 

 rington has shown that the extensor tone of the trunk muscles 

 increases with the bending of the trunk muscles upwards, not 

 downwards. Here there is something parallel with what appears 

 when the neck reflex is produced to raise the latch, for at that 

 time the trunk is raised with the movement of the head upwards. 

 The integration of the trunk muscles, though not clearly observed 

 in the rat when the head is dorsally extended, is evidently present 

 when the act of raising the latch is complete, for then the body of 

 the rat is reflexly held momentarily in a rigid posture before 

 progression begins to the food. Reflex extensor tone in the limbs 

 or the trunk muscles must also exist when, in posturing, the body 

 is set prior to the production of the neck reflex. According to 

 Sherrington reflex extensor tone exists in those muscles that are 

 anti-gravity, and setting of the body at this time, apparently pro- 

 duces an increase in reflex extensor tone in those muscles that 

 prevent excessive crouching, but permit a setting of the body, 

 sufficient to raise the latch. Evidently there is reflex inhibition 

 or relaxation of some muscles, and an increase tonicity in those 



