DIGESTION. 



cles causes the epiglottis to close the passage 

 into the larynx. The muscular fibres of the 

 oesophagus itself are now brought into play, 

 arid by their successive contraction, propel the 

 food from the upper to the lower part of the 

 tube, and thus convey it to its final destination. 

 These three stages, which altogether constitute 

 a very complicated train of actions, are so 

 connected with each other, that the operation 

 appears to be of the most simple kind; it is 

 one of the first that is performed by the newly 

 born animal, and is exercised during the whole 

 period of existence with the most perfect 

 facility.* 



The food, after having thus experienced the 

 action of the first order of parts, which, as we 

 have seen above, is principally, if not entirely, 

 of a mechanical nature, is finally deposited in 

 the stomach. The stomach is a bag of an 

 irregular oval form, which lies obliquely across 

 the upper part of the abdomen, in what is 

 termed, from the presence of this organ, the 

 epigastric region. The structure of the sto- 

 mach, considered in its physiological relation, 

 is threefold. A large portion of it is composed 

 of membranous matter, which gives it its ge- 

 neral form, determines its bulk, and connects 

 it with the neighbouring parts, constituting its 

 external coat. To the interior surface of this 

 coat are attached a number of muscular fibres, 

 by which the various contractile actions of the 

 stomach are performed; these, although not 

 capable of being exhibited as a connected or 

 continuous structure, are considered, accord- 

 ing to the custom of the anatomists, as com- 

 posing the muscular coat, while its internal 

 coat consists of a mucous membrane, which 

 appears to be the immediate seat of the se- 

 creting glands, from which the stomach de- 

 rives its appropriate fluids. But besides this, 

 which may be regarded as the physiological 

 structure of the stomach, by which its parts 

 are so arranged as to give the organ its form 

 and position, its contractile power, and its 

 chemical action, the anatomists have resolved it 

 into a greater number of mechanical divisions, 

 depending principally upon the minuteness to 

 which they have carried their dissections. In 

 this way no less than six or even eight distinct 

 strata or coats have been assigned to the sto- 

 mach. First, the peritoneal covering, which it 

 has in common with all the other abdominal 

 viscera, the dense membrane which more 

 especially gives the stomach its form, called 

 in the language of the older writers the ner- 

 vous coat, two muscular coats,f one composed 

 of longitudinal and the other of circular fibres, 

 and the innermost, or, as it has been termed, 



* For a minute account of the process of deglu- 

 tition generally we may refer to Boerhaave, Prael. 

 t. i. $ 70. .2, Haller's Phys. by Mihles, lect. 23 ; 

 Prim. Lin. cap. 18, $ 607 . . 621 ; El. Phys. xviii. 

 3. 21. . 5 ; Dumas, Physiol. t. i. p. 341. . 353, who 

 divides the act of deglutition into four stages, and 

 to Magendie, Physiol. t. ii. p. 54.. 67, who reduces 

 them to three. 



t Boyer, ubi supra, supposes that the muscular 

 fibres are arranged in three layers. See also 1- 

 liotsou's Physiol. p. 78. 



the villous coat, together with three cellular 

 coats, which are situated between the former 

 and connect them with each other. The ner- 

 vous coat is usually described as being the seat 

 of the glands, as well as of the bloodvessels, 

 nerves, and absorbents which belong to the 

 stomach; but although they cannot perhaps 

 be actually traced beyond this part, there is 

 some reason to suppose that their ultimate 

 destination is on the innermost or villous 

 coat. 



The membranous part of the stomach ap- 

 pears to be peculiarly distensible, so as readily 

 to admit of having its capacity greatly and 

 suddenly increased, in order to contain the 

 large quantity of solids and fluids that are 

 occasionally received into it, while its mus- 

 cular fibres and nerves are possessed respec- 

 tively of a high degree of contractility and 

 sensibility, by which they act powerfully on 

 its contents, propelling them, when necessary, 

 into the duodenum, and thus reducing the 

 bulk of the stomach to its ordinary standard. 

 Besides the mucous fluid which the inner sur- 

 face secretes, in common with all other mem- 

 branes of this description, the stomach is sup- 

 posed to possess certain glands, adapted for 

 the formation of a specific fluid, termed the 

 gastric juice, which acts an important part in 

 file process of digestion ; but the presence of 

 these glands has been rather inferred from their 

 supposed necessity, than from any actual ob- 

 servation of their existence.* 



From the peculiar form and disposition of 

 what have been termed the muscular coats of 

 the stomach, they not only enable the organ 

 to contract in its whole extent and in all direc- 

 tions, but they give to its individual parts the 

 power of successively contracting and relaxing, 

 so as to produce what has been termed its 

 peristaltic or vermicular motion .f The effect 

 produced appears to be, in the first instance, 

 to form in the interior of the stomach a series 

 of folds or furrows, and at the same time to 

 agitate the alimentary mass, so as to bring 

 every part of it, in its turn, within the in- 

 fluence of the gastric juice, while the whole 

 of the mass is gradually carried forwards to- 

 wards the pylorus, and is in due time dis- 

 charged from that orifice. The muscular fibres 

 of the stomach, like all those that are con- 

 nected with membranous expansions, forming 

 what are termed muscular coats, are not under 

 the control of the will. 



In consequence of the great degree of vitality 

 which the stomach possesses, a circumstance in 

 which it is surpassed by scarcely any organ in 

 the whole body, it is very plentifully provided 

 with bloodvessels and with nerves. The arteries, 

 according to the ordinary construction of the sys- 

 tem, are furnished by the contiguous large trunks, 



* Winslow's Anat. Sect. viii. 63..5 ; Hallcr,El. 

 Phys. xix. 1. 14; Bell's Anat. v. iv. p. 58. 



t Haller, El. Phys. xix. 4. 9,0; Boyer, Anat. 

 t. iv. p. 333 . . 5 ; Berlin, Mem. Acad. pour 1760, 

 p. 58 et scq.; this writer appears to have been one 

 of the first who gave us a correct description of t'ae 

 muscular coats of the stomach. 



