ORGANS OF DIGESTION IN THE SHEEP. 141 



wards towards its base ; in the second stage, it is precipitated 

 from the base of the tongue across the orifice of the windpipe 

 into the pharynx : thus the pharynx is concerned in the third 

 or last stage of deglutition, in which stage the gullet also takes 

 a part. 



Gullet. The gullet or oesophagus is the most muscular 

 part of the whole alimentary canal, or, to use an old expres- 

 sion, of the primce vice. The gullet is lined with mucous 

 membrane. Its muscular fibres, as in the ox, are arranged 

 spirally in opposite directions, with turns so close that one 

 partially covers another. These fibres in the sheep may be 

 described as forming two layers, each having an opposite direc- 

 tion. Thus the fibres of the internal layer turn from behind 

 forwards, while those of the external layer turn from before 

 backwards. It was for a long time supposed that this double 

 direction of the muscular fibres in the gullet of the sheep and 

 ox had some reference to the act of rumination ; but it is now 

 ascertained that a similar double arrangement exists in animals 

 that do not ruminate, as in the horse, the cat, the dog, the bear, 

 the seal. 



Blood- Vessels. The several parts of the mouth and throat 

 obtain their nutrition from the blood supplied by branches of 

 the external carotid artery, and, as far as the gullet is con- 

 cerned, by branches from the posterior aorta. For some more 

 particular account of these it will be sufficient to refer to what 

 was said of the arteries distributed to the corresponding parts 

 in the horse (p. 25-29). The same observation applies to the 

 veins and nerves. 



Organs of Digestion in the Abdominal Cavity of the Sheep. 

 The changes which take place on the food in the mouth of 

 the sheep, as in the ox, are principally accomplished after it 

 has been swallowed, and has been subjected for some time to 

 certain operations in the first and in the second stomach, when 



