90 ADVANCED PHYSIOLOGY 



and breast-bone, about one-third of the way down from the 

 shoulders; see Fig. 46. The upper and smaller cavity is called 

 the chest, or thorax, and its principal contents are the heart 

 and lungs. The lower, larger space is the abdominal cavity, 

 which contains the stomach and intestine, the large glands 

 connected with them, and the spleen, kidneys and bladder. 



There are irregular crevices and spaces between these organs, 

 but these are' perfectly filled with the body cavity fluid 

 (coelomic fluid) . 



Nearly all these organs have some muscular tissue in their 

 walls and are continually going through movements; or if 

 they are themselves quiet, they are being constantly rubbed 

 against by neighboring organs which are in motion. This 

 would result in a large amount of friction and irritation, if 

 it were not for the secretions of the serous membrane, which 



forms a delicate lining to both 

 the thoracic and abdominal cav- 

 ities. This lining in the thoracic 

 cavity is called the pleura; that 

 of the abdominal cavity is known 

 as the peritoneum; Fig. 47. Along 

 certain lines, this lining is raised 

 into folds which hang out into the 

 cavities and in these folds the 

 FIG. 47. DIAGRAMMATIC SEC- organs are held. One particular 

 TION ACROSS THE ABDOMEN fold of the peritoneum, called the 

 Showing the relation of the peri- meS entery, is especially large and 



toneum and mesentery. J > . *! r- 



holds the small intestine. This 



complex lining is composed of one-celled glands, constantly 

 secreting a colorless fluid which allows the organs to glide easily 

 over one another or against the walls of the cavity. 



THE STOMACH 



The oesophagus extends down through the thorax as a 

 nearly straight tube, passing through the diaphragm, after 



