392 GENERAL CONSIDERATIONS ON THE DIGESTIVE APPARATUS. 



of a collection of dilatations or tubuliform cavities, which succeed each other 

 from before to behind in the following order : the mouth, jiharynx, mophagus, 

 stomach, and intestine. 



This system of cavities is divided, physiologically, into two principal sections. 

 The first comprises the mouth, pharynx, and oesophagus— the compartments 

 in which are carried on those digestive operations termed preparatory, because 

 they prepare the aliment for the subsequent modifications that constitute the 

 essential phenomena of digestion ; the second section is formed by the stomach 

 and intestines, where these phenomena take place. 



Each of these two sections is furnished in its course with annexed organs, 

 which are present in the majority of Vertebrata ; these are the salivary glands 

 for the cavities of the first category, and the liver, pancreas, and spleen for those 

 of the second. 



In considering the general position of these various parts — principally in 

 Mammals and Birds— it is found that the first section of the digestive canal and 

 its appended organs are lodged beneath the upper jaw and the base of the 

 cranium, and under the cervico-thoracic portion of the vertebral spine. The 

 second section, with its annexes, occupies the great abdominal cavity. 



In Man, these two sections are divided into supra-diaphragmatic and infra- 

 diaphragmatic regions, because of their relations to the diaphragm. 



The constituent parts of the first category might be termed, by reason of 

 their functions, the preparatory organs of the digestive apparatus ; and those of 

 the second, or abdominal portion, the essential organs of digestion. 



These various organs, with those of the respiratory and genito-urinary 

 apparatus, have received the name of viscera, and the term splanchnology is often 

 given to that branch of anatomy devoted to their study.^ 



These new organs differ so notably from those already described, that it is 

 necessary to enter into some generalities as to their nomenclature, arrangement, 

 form, structure, and physical or chemical characteristics. 



Nomenclature in splanchnology does not rest on any scientific basis ; the 

 name of organs being sometimes derived from their form — as the amygdalce ; 

 sometimes from their direction — rectum ; sometimes also from their uses — the 

 oesophagus, salivary glands ; their length — duodenum ; the names of the anatomists 

 who have described them — the duct of Steno, Fallopian tube ; and at times these 

 names are purely conventional, as the spleen. 



They are distinguished as hollow and solid organs. 



1, The HOLLOW ORGANS have a more or less considerable cavity, capable 

 of being increased or diminished, but they are not of a definite shape or size. 

 Their consistency varies with their state of plenitude or vacuity, and they are 

 single or double, symmetrical or asymmetrical. 



In all cases, the walls of the hollow organs are composed of two or more 

 membranes, which we will now describe in a general manner. 



' The designation viscera (from vescor, " I nourish ") has been given to the organs which aid 

 in nutrition, and the term Splanchnology (from trirKdyxvov, a " viscus " or " intestine ") has been 

 bestowed on that division of anatomy which treats of these organs. Splanchnology, thus 

 understood, comprises the study of the digestive, respiratory, urinary, and circulatory apparatus. 

 But the description of the latter forms a separate category, designated, in tiie lauyuago of the 

 schools, Angiolo(iy. On the other hand, however, several authorities im-lude in Splanchnology 

 the organs of generation, and others even add the organs of sense. There is, therefore, no 

 accord in the limits given to tiie definition of Splanchnology ; and this being tiie c«we, we hava 

 thought it best to omit this expression und the distinction souglit to be established by it. 



