1 8 ORGANS OF DIGESTION. 



turn accumulates in animals that take but little exercise, while it 

 is very deficient in such as lead an active life. 



I am induced to believe that the hard knots felt in the abdo- 

 men of such persons as suffer from abdominal affections, fre- 

 quently depend upon the accumulations of the omentum majus 

 at particular but variable points. 



SECT. III. GENERAL ANATOMf OF THE SEROUS MEMBRANES. 



As the peritoneum presents one of the best examples of a nu- 

 merous class of membranes, called SEROUS, it will be useful at 

 this point to inquire into their general condition and properties. 

 They are, for the most part, thin, and strongly resemble com- 

 pressed cellular membrane; having been, indeed, by some ana- 

 tomists, considered as such. They invariably assume the form 

 of perfect sacs, and as they are found in all parts of the body, 

 they are kept distinct from each other. The arachnoid mem- 

 brane of the brain, the pericardium, the pleura, the synovial 

 membranes of the joints, the bursa3 mucosse of tendons, the peri- 

 toneum, and the tunica vaginalis testis, belong to this class. 

 They are not all of the same thickness, as some are much more 

 dense than others; they adhere to neighbouring parts by a la- 

 mina 1 of cellular substance, which is also of variable thickness 

 and ductility; indeed, OR some occasions, it is not entirely dis- 

 tinct, from its extreme shortness and tenuity. 



As the serous membranes are only displayed over the surface 

 of the organs which they cover, after the manner of a double 

 night-cap drawn over the head; their cavity always remains en- 

 tire, notwithstanding it is variously modified by the shape of the 

 organs protruded into it; and has its parietes in contact, owing 

 to external compression. They are entirely distinct from the 

 essential structure of the organs covered, and are displayed over 

 those of the most dissimilar functions, as, for example, the intes- 

 tines and the liver. A sac of this description,, then, is of infinite- 

 importance in establishing between organs which border upon 

 one another a strong partition: and, consequently, in warding off 

 any injurious influence which their dissimilar natures would 

 otherwise cause them to have upon each other. Important or- 

 gans are, therefore, invariably thus insulated, so that whether in 

 s. healthy or in a diseased at ate,, their actions are carried on 



