paralYkSIS of the face. 



569 



nerves be implicated (Fig. 151), the lips will hang loose and 

 motionless ; and saliva will continually trickle from the lower 

 one. As the sufferer has lost the power of prehension with his 

 lips, he will seize his food with his teeth, and will bury his mouth 

 in the water he wishes to drink. We may here note that the 

 horse performs the act of drinking by using his mouth as a 

 suction pump ; the diminution in the pressure of the air contained 

 in the mouth being made by drawing back the tongue. Hence, in 

 order for this pump to act properly, the lips must be firmly closed 



Fig. 151. — Paralysis of lips on both sides. 



together above their point of immersion in the fluid. When 

 paralysis of the lips exists, the animal is obliged to bury his muzzle 

 above the corners of his lips in the fluid, so that fluid, not air, 

 may enter his mouth. 



CAUSES. — As the course of these nerves, from ear to lips, lies 

 almost immediately underneath the skin, they are particularly 

 liable to external injury from blows, use of heavy and ill-fitting 

 bridles, pressure on the head while the animal is held on the 

 ground during operations, and similar causes. In their deeper 

 portions they may suffer from pressure caused by tumours, en- 



