ALIMENTARY CANAL. 495 



splenic omentum, the ascending arid descending meso-colon. The 

 gastro-phrenic ligament is a small xluplicature of the peritoneum, 

 which descends from the diaphragm to the extremity of the reso- 

 phagus, and to the lesser curve of the stomach. The gastro-splenic 

 omentum is the duplicature which connects the spleen to the sto- 

 mach. The ascending mesocolon is the fold which connects the 

 upper part of the ascending colon wrth the posterior wall of the 

 abdomen; and the descending meso-colon, that which retains the 

 sigmoid flexure, in connexion with the abdominal wall. 



Structure of serous membrane. Serous membrane consists of two 

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

 lium. The cellular layer upon its outer surface is rough and vascu- 

 lar, 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 membrane is due 

 to a distinct epithelium, which has been shown by the excellent re- 

 searches of Henle, to be composed of laminae of vesicles, and of 

 flattened polygonal scales with central nuclei, like the epithelium of 

 mucous membrane. Dr. Henle has observed this structure, which 

 may be easily demonstrated with a good microscope upon the sur- 

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

 the lining membrane of arteries and veins, and upon synovial mem- 

 branes. 



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 abso- 

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

 have shown above, the peritoneum in the female is perforated by the 

 extremities 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, pleura?, peritoneum, and tunica; va- 

 ginales, which pour out a secretion containing but a small propor- 

 tion of albumen ; and the synovial membranes and bursse which 

 secrete a fluid containing a larger quantity of albumen. 



ALIMENTARY CANAL.' 



.The Alimentary canalis 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, 





