DIGESTION. 



11 



this anatomists have long been well aware, and 

 it has accordingly been made the object of par- 

 ticular attention, and has even received the ap- 

 pellation of the accessory stomach ; but we shall 

 enter more particularly into the consideration of 

 this subject when we come to treat upon the 

 difference between chyme and chyle, and the 

 nature of the process by which it is effected. 



The peculiarities of the digestive organs in 

 the different classes of animals are interesting, 

 not merely as affording remarkable examples of 

 the adaptation of the animal to the situation in 

 which it is placed, but are especially worthy of 

 our notice on this occasion, as serving to illus- 

 trate the nature of the operation generally, and 

 the mode in which its various stages are related 

 to each other. The most remarkable examples 

 of this kind are the complicated stomachs of the 

 ruminant quadrupeds, and the muscular sto- 

 machs of certain classes of birds.* 



The ruminant animals belong to the class of 

 the mammalia, and are such as feed principally 

 upon the stalks and leaves of plants. The quan- 

 tity of food which they take is very consider- 

 able ; it is swallowed, in the first instance, al- 

 most without mastication, and is received into 

 the first stomach, a large cavity, which is termed 

 the venter magnus, panse, or paunch.^ The 

 food, after remaining for some time in this sto- 

 mach, for the purpose, as it would appear, of 

 being macerated, is next conveyed into the 

 second stomach, a smaller cavity, the internal 

 coat of which is drawn up into folds that lie in 

 both directions, so as to form a number of an- 

 gular cells, from which circumstance it has 

 received the appellation of reticulum, bonnet, 

 or honeycomb. The reticulum is provided 

 with a number of strong muscular fibres, by 

 which the food is rounded into the form of a 

 ball, and is propelled along the oesophagus into 

 the mouth. It is now completely masticated, 

 after having been properly prepared for the pro- 

 cess by its previous maceration in the paunch ; 

 this mastication constitutes what has been 

 termed chewing the cud, or rumination. 



When the food has been sufficiently com- 

 minuted it is again swallowed, but by a pecu- 

 liar mechanism of muscular contraction the 

 passage into the venter magnus is closed, while 

 an opening is left for it to pass into the third 

 stomach, termed omasum, feuillet, ormaniplies ; 

 it is smaller than any of the other cavities, and 

 its internal coat is formed into a series of strong 

 ridges and furrows, but without the transverse 

 ridges of the reticulum. From the omasum the 

 food is finally deposited in the fourth stomach, 

 the abomasum, caillttte, or reed, a cavity consi- 

 derably larger than either the second or third 

 stomach, although less than the first. It is of 

 an irregular conical form, the base being turned 



* For an interesting account of the comparative 

 anatomy of the digestive organs we may refer to 

 Carus's Comparative Anatomy, by Gore, v. ii. p. 72 

 et seq. 



t We have selected the terms by which each of 

 the four stomachs is usually designated in Latin, 

 French, and English respectively , there are, how- 

 ever, various other names -which have been applied 

 to th<m. 



to the omasum ; it is lined with a thick mucous 

 or villous coat, which is contracted into ridges 

 or furrows, somewhat in the manner of the oma- 

 sum, and it appears to be that part of the diges- 

 tive apparatus which is analogous to the single 

 stomach of the other mammalia, where the ali- 

 ment undergoes the process of chymification, the 

 three first stomachs being intended to macerate 

 and grind it down, in order to prepare it for the 

 action of the gastric juice. (See RUMINAFTIA.) 

 Although we conceive that the operation of 

 the different parts of this complicated apparatus 

 is pretty well understood, it still remains for us 

 to inquire into the final cause of the arrange- 

 ment, or why the maceration and mastication of 

 the food in certain classes of animals should be 

 effected in a manner so different from what it is 

 in others, which, in their general structure and 

 functions, the most nearly resemble them. The 

 opinion which was entertained on this subject 

 by the older anatomists, and which may be still 

 regarded as the popular doctrine, is, that the 

 nature of the food of these animals, and the large 

 quantity of it necessary for their support, requires 

 a greater length of time for its comminution and 

 a greater quantity of the mucous secretions than 

 it could obtain by the ordinary process. But 

 although there may be some foundation for this 

 opinion, the more extended observations of 

 modern naturalists show, that it does not apply 

 in all cases, and that there are so many excep- 

 tions to the general rule as to lead us to doubt 

 the truth of the position.* It is to be ob- 

 served, that when animals with ruminant sto- 

 machs take in liquids, the fluid passes immedi- 

 ately into the second stomach,f where it is 

 mixed with the aliment after it has been 

 macerated in the venter magnus, and probably 

 moulds it into the proper form, for its return 

 along the oesophagus into the mouth. While 

 the young animal is nourished by the mother's 

 milk, the fluid is conveyed, in the first instance, 

 through the third stomach into the fourth, and it 

 is not until it begins to take solid food, that the 

 process of rumination is established. It is 

 hence concluded, that the animal possesses the 

 power of conveying the food at pleasure either 

 into the first or the third stomach, and of return- 

 ing it from the second into the mouth ;| these, 

 like many other voluntary acts, being of the 

 kind which are termed instinctive. 



The other kind of stomach which we referred 

 to above as possessing a peculiar structure, 

 and acting on a different principle from that of 

 the human species, is the muscular stomach of 

 certain classes of birds. Birds are not pro- 

 vided with teeth, or with any apparatus which 

 can directly serve for the process of mastica- 

 tion ; yet many of them feed upon hard sub- 

 stances, which cannot be acted upon by the 

 gastric juice, until they have undergone some 

 process, by which they may be comminuted or 

 ground down into a pulpy mass. This is 

 effected by the ingluvies, the craw or crop, and 

 the ventriculus bulbosus or gizzard. The first 

 * Blumenbach's Comp. Anat. p. 138. note 20. 

 t Home, ubi supra, p. 363. 



\ Blumenbach, ubi supra, p. 138. note 18; Ray's 

 Wisdom of God, &c., p. 188. 



