ALIMENTARY CANAL. 559 



meso-colon is the fold which connects the upper part of the ascending 

 colon with the posterior wall of the abdomen ; and the descending 

 mesa-colon, that which retains the sigmoid flexure in connection with 

 the abdominal wall. 



Structure of serous membrane. Serous membrane consists of two 

 layers, an external or nbro-cellular layer, and an internal layer or 

 epithelium. The fibro-cellular layer upon its outer surface is rough 

 and vascular, and adherent to surrounding structures ; but on its 

 inner surface is dense and smooth, and wholly deficient of vessels 

 carrying red blood. The smooth and brilliant surface of serous mem- 

 brane is due to a distinct epithelium, which has been shown by the ex- 

 cellent researches of Henle, to be composed of laminae of vesicles, and 

 flattened polygonal scales with central nuclei, like the epidermis and 

 epithelium of mucous membrane. Dr. Henle has observed this struc- 

 ture, which may be easily demonstrated with a good microscope upon 

 the surface of all the serous membranes of the body, upon the surface 

 of the lining membrane of arteries and veins, and upon synovia! 

 membranes. 



The general characters of a serous membrane are its resemblance to 

 a shut sac, and its secretion of a peculiar fluid, resembling the serum 

 of the blood ; but the former of these characters is not absolutely 

 essential to the identity of a serous membrane ; for, as we have 

 shown above, the peritoneum in the female is perforated by the ex- 

 tremities of the Fallopian tubes ; while in aquatic reptiles there is a 

 direct communication between its cavity and the medium in which 

 they live. 



From the variable nature of the secretion of these membranes, they 

 have been divided into two classes, the true serous membranes, viz. 

 the arachnoid, pericardium, pleurae, peritoneum, and tunicae vaginales, 

 which pour out a secretion containing but a small portion of albumen ; 

 and the synovial membranes and bursae, which secrete a fluid contain- 

 ing a larger quantity of albumen. 



ALIMENTARY CANAL. 



The Alimentary canal is a musculo-membranous tube, extending 

 from the mouth to the anus. It is variously named in the different 

 parts of its course ; hence it is divided into the 



Mouth, 

 Pharynx, 

 (Esophagus. 

 Stomach, 



C Duodenum, 

 Small intestine < Jejunum, 



(^ Ileum. 



C Caecum, 

 Large intestines Colon, 



( Rectum. 



