242 DIGESTIVE SYSTEM. 



pierces the substance of the diaphragm, and enters the stomach, 

 at a rio ht angle, about the centre of its upper and anterior part. 



Structure. — The esophagus presents, externally, a strong, red, 

 muscular coat ; internally, one remarkable for its whiteness, 

 which in its nature is cuticular. The muscular coat is com- 

 posed of two orders of fibres — a longitudinal, forming an out- 

 ward layer; and a circular, an inward layer: the former will 

 shorten the tube, and perhaps dilate it for the reception of food ; 

 the latter, by successive contractions of the canal, will transmit 

 the food into the stomach. The second, or internal coat, is 

 called the cuticular, from its analogy to the cuticle of the skin. 

 Although it is continuous with the membrane of the pharynx, it 

 is of a totally different composition : it is thinner, but it is much 

 more compact and stronger in its texture, and, I believe, is both 

 insensible and inorganic. It adheres to the muscular covering 

 by a fine cellular tissue, the extensibility of which gives full play 

 to the latter; and admits, during the empty or collapsed state of 

 the tube, of the former being thrown into many longitudinal pUccs 

 or folds ; as is demonstrated by making a transverse section of 

 the tube : such appearances result from the contraction of the 

 one coat, and the want of proportionate elasticity in the other. 

 Between the two tunics, embedded amongst the connecting cel- 

 lular tissue, are numerous follicular glands, whose office is to 

 pour forth a mucous secretion upon the internal surface of tlie 

 lining membrane to render the passage of food along it glib and 

 free from any friction. 



OF THE ABDOMEN. 



In consequence of the organs next to be described being con- 

 tained in the cavity of the abdomen, it will be necessary to ex- 

 amine this cavity, in order to understand their relative situation 

 and connexion. 



The abdomen, or belli/, is formed principally of soft parts; 

 which parts consist, in the main, of the four pairs of abdominal 

 muscles (described at page 124) : at least, they constitute its 

 broad superficies below and laterally. Its anterior part (where 

 the most important viscera are situated, viz. the stomach and 

 liver) is bounded at the sides by the false ribs, and in front by 

 the diaphragm; its posterior compartment (containing the organs 

 of generation), by the pelvis ; its superior, by the dorsal and 

 lumbar vertebrae, and muscles belonging to the loins. 



Seeing that the contained organs lie altogether in this cavity, 

 which is one of capacious dimensions and without any natural 

 division in it, anatomists have found it necessary (in order to 



