286 THE STOMACH. 



/ The communication between the stomach and the first intestine. 



g The common, orifice through which the bile and the secretion from the pancreas paet into 



the first intestine. The two pins mark the two tubes here united. 

 h A smaller orifice, through which a portion of the secretion of the pancreas enters the 



intestines. 



THE oesophagus, as has already been stated, consists of a muscular mem- 

 branous tube, extending from the posterior part of the mouth down the left 

 side of the neck, pursuing its course through the chest, penetrating through 

 the crura of the diaphragm, and reaching to and terminating in the stomach. 

 It does not, however, enter straight into the stomach, and with a large open 

 orifice ; but there is an admirable provision made to prevent the regurgitation of 

 the food when the stomach is filled and the horse suddenly called upon to per- 

 form unusually hard work. The oesophagus enters the stomach in a somewhat 

 curved direction it runs obliquely through the muscular and cuticular coats for 

 some distance, and then its fibres arrange themselves around the opening into the 

 stomach. Close observation has showD, that they form themselves into seg- 

 ments of circles, interlacing each other, and by their contraction plainly and 

 forcibly closing the opening, so that the regurgitation of the food is almost 

 impossible. 



The following is a simple but accurate delineation of the structure of the 



termination of the oesophagus, and 

 the manner in which it encircles 

 the orifice of the stomach. We 

 are indebted to Mr. Ferguson, of 

 Dublin, for this interesting dis- 

 covery. 



A microscope of very feeble 

 power will beautifully show this 

 singular construction. It is not 

 precisely either a sphincter muscle 

 or a valve, but it is a strong and 

 almost insuperable obstacle to the 

 regurgitation of the food. The 

 left side of the stomach is in con- 

 tact with the diaphragm. It is 

 pressed upon by every motion of the diaphragm, and hence the reason why the 

 stomach is so small compared with the size of the animal. It is indeed 

 strangely small, in order that it might not press too hardly upon the diaphragm, 

 or painfully interfere with the process of respiration, when the utmost ener- 

 gies of the horse are occasionally taxed immediately after he has been fed. 



At the lower or pyloric orifice, the muscles are also increased in number and 

 in size. These are arranged in the same manner, with sufficient power to 

 resist the pressure of the diaphragm, and retain the contents of the stomach 

 until they have undergone the digestive process. 



The situation of the stomach will at once explain the reason why a horse is 

 so much distressed, and sometimes irreparably injured, if worked hard imme- 

 diately after a full meal. The stomach must be displaced and driven back by 

 every contraction of the diaphragm or act of inspiration ; and in proportion to 

 the fulness of the stomach will be the weight to be overcome, and the labour 

 of the diaphragm, and the exhaustion of the animal. If the stomach is much 

 distended, it may be too weighty to be forced sufficiently far back to make room 

 for the quantity of air which the animal in a state of exertion requires. 

 Hence the frequency and labour of the breathing, and the quickness with 

 which such a horse is blown, or possibly destroyed. Hence also the folly of 



