SEROUS COAT. 5/3 



flexure to the rectum, around which they spread out and form a thick 

 and very muscular longitudinal layer. The circular fibres in the 

 caecum and colon are exceedingly thin; in the rectum they are 

 thicker, and at its lower extremity they are aggregated into the thick 

 muscular ring which is known as the internal sphincter ani. 



SEROUS COAT. The pharynx and oesophagus have no covering of 

 serous membrane. The alimentary canal within the abdomen has a 

 serous layer, derived from the peritoneum. 



The Stomach is completely surrounded by peritoneum excepting 

 along the line of junction of the great and lesser omen turn. The first 

 or oblique portion of the duodenum is also completely included by 

 the serous membrane with the exception of the points of attachment 

 of the omenta. The descending portion has merely a partial covering 

 on its anterior surface. The transverse portion is also behind the 

 peritoneum, being situated between the two layers of the transverse 

 meso-colon, and has but a partial covering. The rest of the small 

 intestine is completely invested by it, excepting along the concave 

 border to which the mesentery is attached. The ctecum is more or 

 less invested by the peritoneum, the more frequent disposition being 

 that in which the intestine is surrounded for three-fourths only of its 

 circumference. The ascending and the descending colon are covered by 

 the serous membrane only in front. The transverse colon is invested 

 completely, with the exception of the lines of attachment of the 

 greater omentum and transverse meso-colon. And the sigmoid flexure 

 is entirely surrounded, with the exception of the part corresponding 

 with the junction of the left meso-colon. The upper third of the 

 rectum is completely enclosed by the peritoneum ; the middle third 

 has an anterior covering only, and the inferior third none what- 

 soever. 



Vessels and Nerves. The Arteries of the alimentary canal, as they 

 supply the tube from above downwards, are the pterygo-palatine, as- 

 cending pharyngeal, superior thyroid, and inferior thyroid in the neck ; 

 oesophageal in the thorax ; gastric, hepatic, splenic, superior and in- 

 ferior mesenteric in the abdomen ; and inferior mesenteric, iliac, and 

 internal pudic in the pelvis. The veins from the abdominal alimen- 

 tary canal unite to form the vena portaa. The lymphatics and lacteals 

 open into the thoracic duct. 



The Nerves of the pharynx and oasophagus are derived from the 

 glosso-pharyngeal, pneumogastric, and sympathetic. The nerves of 

 the stomach are the pneumogastric and sympathetic branches from the 

 solar plexus ; and those of the intestinal canal are the superior and 

 inferior mesenteric and hypogastric plexuses. The extremity of the 

 rectum is supplied by the inferior sacral nerves from the spinal cord. 



