22 THE PERITONEUM. 



or by languid absorption, dropsy may take place in any one of 

 what are called the serous cavities of the body. There is not 

 in fact, though the term is in general use, any cavity or unoc- 

 cupied space in the interior of any of these membranes. In 

 the healthy state, organ is in contact with organ, and the 

 reflected membranes with which they are lined, slide over those 

 which line the parietes of the so called cavities. And when 

 the area of a joint is suddenly enlarged, as those of the fingers 

 may be by pulling at the phalanges, the fluid within becomes 

 rarified to fill the vacuum, and is the cause by its sudden con- 

 densation of the snapping noise heard when the bones return in 

 contact. The same phenomenon is sometimes observed in mas- 

 tication, produced by the relaxation of the ligaments of the 

 temporo-maxillary articulation. 



— Though no nerves have been traced satisfactorily to the 

 serous membranes, and they appear to possess little or no sen- 

 sation in a physiological state, they become exquisitely sensitive 

 when suddenly inflamed, as in pleuritis. The free polished 

 surface of the serous membranes is shown by the microscope 

 to be covered with a very delicate pavemented or tesselated 

 epithelium. In no other part of the human body, according to 

 Henle, but the ventricles of the brain, has the epithelium of 

 serous membranes been found provided with cilia. — 



Of the Peritoneum. 



The abdomen, constructed and occupied as above described, 

 is lined by a thin firm membrane called Peritoneum, which 

 is extremely smooth on its internal surface, and is imme- 

 diately connected with the cellular substance exterior to 

 it. This membrane adheres closely to the anterior, lateral 

 and superior portions of the surface of the abdomen ; and is 

 extended from the posterior surface so as to cover more or less 

 completely, the viscera of the cavity. 



Those viscera which are in close contact with the posterior 

 surface of the abdomen, as some portions of the large intestine, 

 are covered only on their anterior surfaces, and are fixed in 



