O- HTMAN PHYSIOLOGY 



to the digestive system. The central feature of this 

 system is the alimentary canal which, as a matter of f 

 is not strictly confined to the abdominal cavity since it 

 begins at the mouth, extends through the thorax, and 

 at its lower termination traverses the pelvis to open at 

 the anus. Nevertheless, the great part of the digestive 

 tract is in the abdomen. The liver and the pane: 

 are appended to the canal and the spleen is associated 

 with it though perhaps less directly. The kidneys are 

 exposed to view when the organs of digestion are re- 

 moved from the abdominal cavity; they lie behind the 

 peritoneum and are best thought of as belonging to the 

 back rather than to the abdomen. 



In the pelvis there are found the terminal portion of 

 the alimentary canal, as already noted, the urinary 

 bladder, and the reproductive organs. The peritoneum 

 intervenes between the pelvic cavity and that of the 

 abdomen above. Details will be added as we discuss 

 the particular organs which have merely been mentioned 

 at this place. 



Anatomical Terms. It will be well to define here a 

 few terms of anatomy which must often be used. Right 

 and left have their ordinary meaning. Dorsal signifies 

 toward the back and ventral is its opposite (venter, the 

 belly). There is an unfortunate confusion in regard to 

 the employment of anterior and posterior. They have 

 been much used as though equivalent to ventral and 

 dorsal respectively. But another usage which appears 

 more desirable is to define anterior as toward the head, 

 posterior being the reverse. Anterior is then the same 

 as superior, posterior is synonymous with inferior. If 

 we adhere to the practices outlined we shall have no 

 difficulty in comparing the structural relations in the 

 lower animals with those in man. Such difficulty is 

 experienced where the other significance is given to 

 anterior and posterior; as an animal walks the anterior 

 parts precede the posterior but in the erect position the 

 ventral precedes the dorsal. 



