122 VETERINARY PHYSIOLOGY 



comparative ease, the head is rotated backwards and forwards 

 in the plane of the canal. If the labyrinth on one side is 

 removed, rotation to that side from overaction of the 

 labyrinthine mechanism on the opposite side occurs. It is, 

 however, soon recovered from. The same result follows 

 section of the vestibular nerve. 



(2) Stimulation of one of the canals by electricity in the 

 cartilaginous fishes causes movements of the eyes and fins 

 as if the animal were being rotated in the plane of the canal 

 stimulated. 



Injury to a canal causes loss of control of the group of 

 muscles which govern the movements of the head round the 

 axis of that canal. Overaction, on the other hand, causes 

 muscular adjustments to counteract movements round the 

 same axis. 



Such a mechanism might be called into play either — 



(1) By the position of the head in space. 



(2) By the movements of the head. 



(1) That the position of the head in space acts is in- 

 dicated by (rt) the experiments of Kriedl upon the shrimp 

 Palinurus. When this creature casts its shell it also casts 

 its otic vesicle with the contained grains of sand that act as 

 otoliths, and, when its new shell is grown, it inserts particles 

 of sand into the vesicles. By supplying it with particles of 

 iron, Kriedl compelled it to insert these, and when, by 

 means of a magnet, they were brought into contact with 

 different parts of the vesicle, ihe animal took up different 

 positions. 



Qj) The static action of the labyrinths is further shown 

 by the production of definite postures in decerebrated cats, 

 by placing the head in different positions (p. 88). It is also 

 shown by the production of apnoea, absence of breathing, in 

 ducks, by placing the head in certain positions, e.g. directed 

 straight down in the diving position. Another element — a 

 proprioceptive reflex from the joints of the cervical vertebrae 

 ■ — plays a secondary part in these adjustments. 



These static actions probably depend upon the part of 

 the nerve terminations in the utricles and saccule upon 



