406 JOHN LINCK ULRICH 



flexes associated with the movements of the head. A review of 

 the literature on the physiology of reflexes showed that within 

 recent years there have been conducted a number of investiga- 

 tions of the reflexes evoked in decerebrate animals with a change 

 in the position of the head in space. Very few experiments have 

 been made with living animals. Magnus and de Kleijn (10, 11) 

 working with decerebrate rabbits, cats, and dogs have isolated 

 definite reflexes. With passively changing the position of the 

 head in relation to the body, continuous excitations in the laby- 

 rinth of the ear evoke movements of all four limbs. A change in 

 the position of the labyrinth in space and the position of the neck 

 in regard to the body, increases in decerebrate rigidity, the tonic 

 condition of the limbs. 



When the head is raised, the lower jaw forming an angle of 45 

 degrees with the midline of the body, the extensor tone of the 

 fore limbs increases, and that of the hind limbs decreases at times 

 into flexor tone. When the head is lowered to within 45 degrees 

 of the midline of the body, the reverse conditions are produced, 

 the extensor tone of the hind limbs increases and that of the fore 

 limbs decreases, sometimes into flexor tone. On the other hand 

 there arises, when the head is bent to the left or to the right, or 

 when the head is twisted in either of these directions, an increase 

 extensor tone of the fore limbs on the side from which the head is 

 bent and a decrease in tone, often amounting to flexion, on the 

 side to which it is bent. 



Magnus and de Kleijn call the first of these reflexes, those 

 derived by changing the position of the head in space, the laby- 

 rinth reflexes, and the other two, derived by bending of the neck 

 in regard to the position of the body, neck reflexes. Sherrington 

 (12), who has also investigated these reflexes, regards such mani- 

 festations of increase extensor tone as modifications of reflex 

 posture of standing decerebrate rigidity. For when the head of 

 the standing decerebrate preparation is raised dorsally, the pos- 

 tural contractions of the fore limbs increase and the fore quarters 

 are raised, whereas the postural contractions of the hind limbs 

 are inhibited, flexed, and the hind quarters lowered. The reverse 

 is the case when the head is passively flexed; the postural con- 



