AN ATOM!. 



'equently does not interfere with the pas- 

 sage of the air into the wind-pipe. In the 

 act of swallowing-, the tongue is carried 

 backwards, and the wind-pipe is drawn 

 up : hence the epiglottis becomes me- 

 chanically applied over the opening, and 

 at this moment the food enters the pha- 

 rynx over it, and by its pressure closes the 

 aperture still more completely. As soon 

 as the food has passed, the tongue and 

 wind-pipe resume their former position, 

 the elasticity of the cartilage restores it 

 to the erect state, and the glottis is again 

 free for the continuance of respiration. 

 So completely does this simple mechan- 

 ism answer the proposed end, that, al- 

 though even r morsel of food passes over 

 the glottis, the accident of any portion 

 going the wrong way, as it is termed, is 

 comparatively "rare, and can only arise 

 from our being imprudent enough to 

 laugh or talk while we are swallowing. 

 In either of these cases air must pass out 

 of the trachea, and, by so doing, it lifts 

 up the epiglottis. 



The pharynx opens below in the oeso- 

 phagus, a muscular tube, which conveys 

 the food into the stomach. The aliment, 

 in its farther progress, goes through dif- 

 ferent viscera contained in the abdomen ; 

 and we shall therefore proceed with a de- 

 scription of that cavity. * 



The term abdomen includes a large 

 portion of the body. It is bounded above 

 by the cartilages of the ribs, and by the 

 diaphragm, which separates it from the 

 chest, at the back part, by the bodies of 

 the lumbar vertebra ; in front and at the 

 sides, by the abdominal muscles ; and be- 

 low, by the bones of the pelvis. 



It is every where lined by a membrane 

 called the peritoneum. The surface of 

 this is perfectly smooth and polished, and 

 moistened by a serous exhalation produ- 

 red by the minute arteries of the part. 

 This membrane not only lines the cavity 

 of the abdomen, but also covers all the 

 viscera contained in that cavity, so that 

 the exterior surface of each part consists 

 of what anatomists call its peritoneal coat. 

 Hence the motions of these parts upon 

 each other, and upon the surface of the 

 cavity, are performed with perfect facility. 

 The productions of the membrane, 

 which gives these exterior investments 

 to the viscera, serve also to confine them 

 in their relative positions. 



The cavity is subdivided into three re- 

 gions, the epigastric, which includes all 

 the space above an imaginary line drawn 

 across the belly,from the greatest convexi- 

 tieq of the cartilages of tne seventh true 



rib; the umbilical, which is the division 

 between this line and another drawn from 

 the anterior superior spines of the ilia ; 

 and the hypogastric, which is the space 

 left below the last line. 



The sides of the epigastric region, 

 which are the spaces covered by the car- 

 tilages of the ribs, are called hypochon- 

 dria : the sides of the umbilical region are 

 named the loins : and those of the hypo- 

 gastric the groins. 



The stomach is a large membraneous 

 reservoir, receiving the food from the oeso- 

 phagus, and retaining it until a certain 

 change, called digestion, is produced. Its 

 figure is conical, as it is largest at the left 

 end, and gradually decreases in size to- 

 wards the right: these are called the great- 

 er and smaller extremities of the stomach. 

 It is also bent in its course, so that we 

 describe a greater and smaller curvature 

 or arch. It has two openings, one close 

 to the diaphragm, called the cardiac, su- 

 perior, or oesophageal ; the other, just at 

 the smaller end, is called the pylori c, or 

 lower orifice. The capacity of the sto- 

 mach varies from about 5 to 11 pints. 



Its structure is muscular ; and this is 

 necessary in order to propel the food 

 when digested. Under the muscular coat 

 is found the internal, or villous, tunic ; the 

 arteries of which pour out the gastric 

 juice, the chief agent in the digestion of 

 the food. 



The pylorus, which word is derived 

 from two Greek terms, signifying the 

 keeper of the gate, is a contracted ring, by 

 which the stomach communicates with the 

 small intestiqe. It prevents the food from 

 passing out of the stomach before it has 

 been sufficiently acted on by the gastric 

 juice, 



The stomach receives a portion of peri- 

 toneum as the oesophagus passes the dia- 

 phragm. There is also a process coming 

 from the liver, called the lesser omentum, 

 or mesogaster. This is attached to the 

 lesser arch of the stomach. The great 

 omentum, or the caul, is affixed to the 

 greater arch of the stomach, and hangs 

 from thence over the surface of the intes- 

 tines, being interposed between them and 

 the parietes. It is also attached to a part 

 of the colon : its use is unknown. 



The small intestine is divided into three 

 parts; the duodenum, jejunum, andileum; 

 but this distinction is an arbitrary one, and 

 not founded on any difference in struc- 

 ture. It consists of a membranous tube, 

 about an inch, or an inch and a half in di- 

 ameter, and four times the length of the 

 subject. Notwithstandingthis great length, 

 it is collected, by means of numerous turn- 



