It appears, indeed, to be the part which is subservient to the important process of chylification, while the office of the jejunum and ilium is principally confined to abstracting the chyle from the residual mass; this is accomplished by its being gradually transmitted along their cavity, thus permitting the lacteals to absorb the nutritive part, as it is brought into contact with their orifices. The means by which the absorption is effected, will be considered in the following chapter.

In the course of this work, I have confined my attention for the most part, to the functions as they exist in man, and in the animals which the most nearly resemble him, with only occasional observations on comparative physiology. There are, however, some remarkable deviations from the ordinary form and action of the digestive organs, even among the higher classes of animals, of which I shall give a more particular description, not only in consequence of the interest which may be attached to them considered individually, but more especially, from the information which they afford us concerning the function of digestion generally, by noticing the peculiarities of their structure, and observing the relation which their several parts bear to the operations of the human organs. I refer to the compound stomachs of the ruminating animals, and to the strong muscular stomachs of certain birds.

§ 19, 0; see Sabatier, Anat. t. ii. p. 302, 3; Boyer, Anat. t. iv. p. 345; Chaussier, in Dict. des Scien. Med. v. ix. p. 429..4; and Dumas, Physiol. t. i. ch. 10.

Many of the mammalia possess a stomach of a much more complicated structure, and possessed of a much greater variety of distinct parts, than that of man. These animals feed principally on the leaves or stalks of plants, which they take in large quantity; the food is swallowed, in the first instance, without much mastication, and is received into a capacious cavity, called venter magnus, or paunch, where it remains for some time, as if for the purpose of being softened or macerated. Connected with this is a much smaller cavity, which, in consequence of its internal coat being drawn up into folds, that lie in both directions, so as to leave between them. a series of angular cells, has obtained the name of reticulum, or honey-comb. From this second stomach the food is again brought up into the mouth, in the form of a rounded ball, and is then masticated by the animal, until it is sufficiently comminuted, constituting the process of rumination, or chewing the cud. The mass, when duly prepared, is again swallowed; but it now passes by the first and second stomach, and is conveyed into the third cavity, called omasum, or maniplies, distinguished by the broad folds or ridges of the inner membrane, which are disposed longitudinally, and differ from those of the reticulum, in not being crossed by others in the contrary direction; it is also of smaller size than any of the other cavities. into the fourth stomach, named abomasum or read, which is of a larger size, although much less than the paunch, is of an irregular conical form, the base

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From this the food is sent

2 G

being turned towards the omasum, lined with a mucous or villous coat, which is disposed into ruga like those of the third, and appearing, in its structure and funetions, to be most analogous to the simple stomach of man and the other mammalia.

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We have a very complete account of the digestive organs of ruminant animals by Peyer in his Mericologia; they are described, as it appears, with great minuteness, accompanied with coarse, but expressive engravings. We have excellent views of the parts by Daubenton, in Buffon's great work, Nat. Hist. des Anim. t. iv, pl. 15..8, and by Sir Ev. Home in Phil. Trans. for 1806, p. 362.:5, pl. 15 and 16; and Lect. Comp. Anat. v. ii. pl. 21..25. See also Haller, El. Phys. xix. 1. 2; and xix. 4. 15; and Cuvier, Leç. Anat. Comp. t. iii. p. 363..6. Among the older physiologists we have a good description of the parts by Fabricius, in his treatise "De Varietate Ventricu lorum;" Op. p. 128. et seq. The reader may consult with ad vantage Grew's work on the Compar. Anat, of the stomach, a treatise, which in a short compass, contains many valuable, and probably original observations, respecting the comparative anatomy of the digestive organs; also Glisson, de Ventriculo, Ch. i. § 9.. 15, p. 123,.7. There are certain animals which appear to possess a kind of intermediate stomach, between the simply membranous receptacle, and the complicated structure of the ruminants. This is particularly the case with the horse, in which the two halves of the stomach possess an obviously different structure, the left side seeming to be intended merely as a reservoir for the food, while the right half is provided with the villous coat and the glandular apparatus to adapt it for the purpose of chymification; Bertin, Mem. Acad. Scien. pour 1746, p. 23, et seq.; fig. 2, Blumenbach, Comp. Anat. § 87, p. 133. and note C. P. 153. From the remarks of Prof. Monro it appears somewhat doubtful how far this structure exists in the human stomach, as has been supposed by some physiologists; Outlines, v. ii. p. 111..5. Hunter informs us that the whale possesses

There is some doubt as to the effect which is produced by the different parts of this complicated apparatus, and as to the use which they serve in the œconomy of the animal. It is, however, pretty clear that the object of the first stomach is principally that of maceration, which is still further completed in the reticulum, that this cavity as well as the omasum contain secretions which are mixed with the aliment, which it may be presumed are more or less similar to the saliva, while it is in the abomasum that the proper digestive operation, that of chymification, is conducted. There has been much discussion concerning the final cause of this arrangement, or concerning the cause why the maceration and mastication of the food is effected in a different manner in these animals from what it is in those that, in other respects, the most nearly resemble them. The popular opinion is, that, from the nature of their food, the large quantity of it which these animals require for their support, and the consequent length of time which is necessary for its complete mastication, it was requisite that it should be more completely macerated, and be mixed with a greater proportion of the different mucous secretions, than is the case in the or

four stomachs, which in their structure and appearance bear a considerable resemblance to the digestive organs of the ruminants; but it appears that they do not correspond in their uses, as in this class of animals the second cavity seems to be that in which chyme is produced; Phil. Trans. for 1787, p. 410, 1. 9 Hunter on the Animal Economy, p. 212, 3.

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dinary process. It has, however, been doubted how far this hypothesis can be maintained, as there are some of the ruminant animals, where the organs of mastication, as well as the general habits of the animal, would appear to be adequate to the preparation of the food by means of a simple stomach. When animals that possess ruminant stomachs take in liquids, they are conveyed in the first instance into the second stomach, where they serve to macerate the food as it passes from the paunch, so as to prepare it for the of rumination. While the young animal is process nourished altogether by the mother's milk, it passes directly through the third into the fourth stomach, and it is not until they begin to eat solid food that rumination is established. It has been supposed that the act of rumination is under the control of the will, and that the animals possess a voluntary power of conveying the food at pleasure either into the first or the fourth stomach, and of returning it from the third stomach into the mouth.*

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It was supposed by some of the ancient anatomists, as it appears by Galen and Aristotle, that the use of this particular organization of the stomach, was to compensate for the deficiency of the incisor teeth, the materials of which are applied to the formation of the horns. See remarks upon this opinion by Fabricius, de Variet. Ventr. Op. p. 131, 2.

2 Blumenbach, Comp. Anat. by Lawrence, p. 134. . S.

3 Home in Phil. Trans. for 1806, p 363.

4 Grew, Comp. Anat. of the Stomach, &c. Ch. v. p. 26; Ray's Wisdom of God, &c. p. 275; Blumenbach, Comp. Anat. § 90, 1. p. 137, 8. The mechanism of these parts, as connected with