ORGANS OF DIGESTION. 411 



thick muscular valvular folds across the opening of com- 

 munication, by the closing of which a canal is formed 

 which leads to the third cavity of the stomach. 



The paunch receives the crude-unmasticated vegetable food 

 collected in large quantity while the animal is erect and grazing, 

 and the process of rumination generally commences when this 

 cavity is filled, and the animal is reclining at rest. In rumi- 

 nation, small portions of the unmasticated food, moistened 

 and softened in the paunch, pass into the second cavity to 

 be sent by its contraction, as a bolus, upwards through the 

 muscular oesophagus to the mouth. After being thoroughly 

 masticated and salivated in the mouth, the bolus returns, as 

 a soft pulp, by the oesophagus ; and, its stimulating quality 

 being now altered, it finds the two valvular folds at the 

 lower end of the oesophagus closed, and shortened by con- 

 traction, and is directed by the short canal they thus form, 

 into the third, and thence into the fourth cavity of the sto- 

 mach. The third or foliated stomach (omasum) is generally 

 the shortest and smallest, though elongated and narrow in 

 the camelus and auchenia (130. A. d.), and is provided in- 

 ternally with numerous longitudinal, alternately small and 

 large folds, having their free margins directed to the centre 

 of the cavity. The second and third cavities have their mu- 

 cous membrane covered with small villi and distinct epithe- 

 lium, like those lining the first stomach. The third cavity 

 leads directly to the fourth or abomasum (130. A. e.) which 

 is next in capacity to the paunch, lined with a soft highly 

 vascular mucous coat, provided internally with large longi- 

 tudinal folds, and apparently destitute of epidermic lining. 

 The structure and form, and secretions of this fourth cavity, 

 placed on the right side of the others, render it the proper 

 digestive stomach, and the most analogous to the single di- 

 gestive sac of carnivorous and higher quadrupeds. 



In the camels, dromedaries and lamas, numerous rows 

 of large, quadrangular, deep water-cells are developed on 

 the parietes of the second stomach, and on the parts of the 

 paunch next to that cavity. These cells are surrounded by 

 muscular fibres which, by their contraction, are capable of 

 excluding the food from the water-cavities ; and by the gra- 

 dual opening of the cells, the water is allowed to mix in 

 successive small portions with the digesting aliment. These 

 animals are thus enabled to convey and economise a large 



