410 JOHN LINCK ULRICH 



are not so often localized as this description may indicate, for 

 the integrated reflexes of any animal are coordinated. 



When the functional condition of the reflex extensor thrusts 

 can be said to be the best, and reflex excitability manifest, pas- 

 sively bending the head and the neck to the right and to the left 

 or extending the head dorsally to the midline of the body or 

 within 45 degrees of this line, evokes extension and flexion of the 

 fore limbs with concomitant changes in the hind limbs and the 

 tail. Passively bending the head to the right evokes an extensor 

 thrust of the left ipsilateral fore limb and flexion of the right con- 

 tralateral fore limb extension of the right contralateral hind 

 limb and flexion of the left ipsilateral hind limb; the reverse of 

 these conditions is obtained when the head is passively bent to 

 the left, for then extension of the right ipsilateral fore thrust 

 with flexion of the left and extension of the left contralateral 

 hind limb with flexion of the right ipsilateral hind limb occurs. 

 The tail is raised dorsally and frequently inclined in the 

 direction in which the head is bent; dorsally extending the 

 head evokes extension of both fore limbs and flexion of the hind 

 limbs with contractions and extension of the trunk muscles. 

 Extending the tail dorsally evokes extensor thrusts of both hind 

 limbs and flexion of the fore limbs. Thus as previously stated 

 rhythmic extension and flexion may occur in all limbs, instead 

 of the evoking of independent extensor thrusts. 



These extensor thrusts in the rat's limbs are in a way practi- 

 cally the same as the increase extensor tone observed to take place 

 in decerebrate cats and dogs, for they are conditioned by similar 

 excitations and similar antagonistic muscles of the limbs are in- 

 volved. In the living animal the increase tone is revealed in ex- 

 tension and flexion of the limbs, and in decerebrate forms in the 

 increase tone of decerebrate rigidity. The direction of extension 

 of the limbs is in the two cases also different. The increase tone 

 in the decerebrate animals extends the limbs directly downward 

 or outward in accordance with the position in which the animal 

 is placed, whether resting on the back or in a standing posture; 

 in the living rat, the direction of the fore extensor thrust when 

 head is moved is in the direction in which the head is passively 



