326 GENERAL CONSIDERATIONS ON Till: DKlKXTIVE APPARAT 



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

 tions : the first comprises the mouth, pharynx, and oesophagus, or the compart- 

 ments in which are carried on those digestive operations termed " preparatory," 

 because they prepare the aliment for the subsequent modifications which 

 constitute the essential phenomena of digestion ; the second section is 

 formed by the stomach and intestine, 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 yliunlx 

 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 is lodged beneath the upper jaw and the 

 base of the cranium, and under the cervico-thoracic portion of the vertrhnil 

 column. The second section, with its annexes, occupies the great abdominal 

 cavity. 



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

 infra-diaphragmatic, 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 composing the respiratory and genito- 

 urinary apparatus, have received the name of viscera, and the term splanch- 

 nology is often given to that branch of anatomy devoted to their study. 1 



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

 is necessary to enter into some generalities as to their nomenclature, dis- 

 position, 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 amygdnlce ;" 

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

 oesophagus, salivary glands ; their length duodenum ; the names of the anato- 

 mists who have described them the duct of Stenon, Fallopian tube; and 

 at times these names are purely conventional, as the spleen. 



They are distingxiished 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 

 volume. Their consistency varies with their state of plenitude or vacuity, 

 and thoy are single or double, symmetrical or asymmetrical. 



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

 membranes which we will now describe in a general manner. 



a. The innermost is called the MUCOUS MEMBRANE, because of the mucus 

 with which its free surface is always covered. It is made continuous with the 

 skin at the natural openings ; and from its similarity of organisation it has 

 been named the internal or re-entering skin, or internal tegumentary niemlrnin: 



1 The name of viscera (from vescnr, I nourish) lias been given to the organs which aid in 

 nutrition, nnd the term Splanchnology (from aityJ^xvov, a viscus or intestine) has been 

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

 imdi-ratoud, comprises the study of the digestive, respiratory, urinary, and circulatory 

 apparatus. But the description of the latter forms a separate category, designated in the 

 language of the schools by the name of Amjioloiiy. On the other hand, however, several 

 authorities include in Splanchnology the organs of generation, and others even add tli- 

 organs of sense. There is, therefore, no accord in the limits given to the definition of 

 Sjilunchnoloyry ; and this "being the case, we have thought it best to omit this expression 

 and the distinction it seeks to establish. 



