24 PHYSIOLOGY AT THE FARM. 



pair of scissors. In animals of this description the cavity in 

 the squamous portion of the temporal bone is deep, and is 

 directed forwards, while it is so bounded by an anterior and 

 posterior bony eminence, that the condyle of the jaw received 

 into it can move only in one direction. In herbivorous 

 animals, on the contrary, the glenoid cavity is shallow, per- 

 mitting a great extent of movement to the condyle ; and this 

 is the case in the horse. Thus, besides the hinge movement 

 common to all mammals, there is a power of moving the jaw 

 forwards, backwards, and laterally movements of essential 

 effect in grinding the food to a proper degree of comminution. 

 The temporal and masseter muscles, which belong to the ex- 

 ternal aspect of the head, are those concerned in the hinge- 

 like motion of the jaw ; while the pterygoid muscles, lying 

 on the inner side of the jaw, on each side, and acting not 

 together on the opposite sides, but alternately, produce the 

 grinding movements. 



Pharynx and Gullet. A short notice of the pharynx and 

 gullet will permit the act of deglutition to be taken along with 

 the changes on the aliment in the mouth. 



The pharynx is the muscular pouch behind the veil of the 

 palate, into which the masticated food passes from the mouth 

 to be immediately transmitted to the gullet. It has a conical 

 form, the smaller end being below, where it meets the gullet, 

 and is lined by a mucous membrane. The muscular fibres are 

 attached to the neighbouring bones, and are so disposed as, by 

 their contraction, to narrow the whole cavity of the pouch, by 

 which action the mass is directed downwards. 



The gullet is continued down from the pharynx. It is a 

 powerfully muscular tube lined by mucous membrane. As it 

 descends in the neck it inclines a little to the left side, and, 

 finally, is found altogether to the left side of the windpipe. It 

 passes through the chest between the two sacs of the pleura, 



