56 NUTRITIONAL PHYSIOLOGY 



are the thoracic cavity above the diaphragm and within 

 the cage of the ribs, the abdominal cavity below the dia- 

 phragm, and the much smaller pelvic cavity bounded by 

 the bones of the hip girdle. When we speak of these as 

 cavities we do not mean that they contain any air-filled 

 space. They are completely filled by the organs which 

 they enclose plus a small quantity of fluid. Hence they are 

 only potential cavities in life, becoming actual when their 

 contents are removed in course of dissection. The thoracic 

 cavity contains the lungs, nearly surrounding the heart, 

 and is traversed by the esophagus. The abdominal cavity 

 is filled almost entirely by the organs of digestion the 

 stomach, the small and large intestines, the liver, and the 

 pancreas. The spleen at the left of the stomach is less 

 certainly connected in its functions with the alimentary 

 system. The kidneys lie in the dorsal body wall rather 

 than in the abdomen. In the small pelvic cavity are the 

 urinary bladder, the terminal part of the large intestine, 

 and the reproductive organs. 



The mouth, the first division of the alimentary canal, 

 scarcely calls for detailed description. Above, a bony par- 

 tition separates it from the intricate spaces of the nasal 

 passages. At the back this "roof" is prolonged as a 

 mobile, muscular curtain the soft palate. Below the 

 edge of the soft palate a region is reached which is common 

 to the alimentary and respiratory systems. This segment 

 of the canal is known as the pharynx, though the term is 

 extended also to the space behind the soft palate, which is 

 above the normal course of food. The teeth and the 

 tongue with its wonderful muscular development are suffi- 

 ciently obvious. JDucts from the salivary glands open 

 into the mouth. We are rarely conscious of the situation 

 of these openings, though in the dentist's chair we may 

 notice the rapid flow of saliva from one which is opposite 

 the upper molars. This is the place of entrance of the 

 secretion of the parotid glandj situated before and below the 

 ear, the gland usually affected in mumps. Under the 

 tongue and within the sweep of the lower jaw-bone there 



