376 CLINICAL APPLIED ANATOMY. 



which is itself a derivative of the fore gut. The occlusion is 

 usually just below the level of the cricoid cartilage, and is deter- 

 mined by the outgrowth of the lung bud from the primitive 

 intestinal tube. A fistulous communication between the oeso- 

 phagus and trachea frequently exists below the obstruction. 

 Barely the oesophagus is stenosed just above its entrance into 

 the stomach. 



Hypertrophic stenosis of the pylorus is probably a congenital 

 condition, and is characterised by a great hypertrophy of the 

 muscular coat of the pylorus and pyloric canal. 



Occlusion or obstruction of the duodenum is sometimes found 

 in the neighbourhood of the common bile duct, and may be due 

 to the outgrowth of the liver, or pancreas buds in this position. 



Stenosis of the duodeno-jejunal flexure is rare. It has been 

 attributed to developmental changes in the peritoneal folds of 

 this region. 



Occlusion or stenosis of the ileum may be found at the site of 

 Meckel's diverticulum. This diverticulum arises within three 

 feet of the ileo-csecal valve, and is the residue of the vitelline 

 duct. It may or may not retain its connexion with the umbilicus. 



Multiple congenital strictures of the small intestine occur 

 rarely. No satisfactory explanation of these has been offered. 



Congenital dilatation of the colon is associated with obstinate 

 constipation, and may be met with without organic obstruction 

 of the rectum or anus. 



Malformations of the rectum include congenital strictures, 

 imperforate conditions, absence of the anus or the rectum, or 

 both those structures, and openings of the rectum in abnormal 

 situations. 



An obstruction may be found at the junction of the anus and 

 rectum in the form of a membranous fold. The fold is probably 

 a remnant of the cloacal membrane. The anal valves, which lie 

 at the lower ends of the columns of Morgagni, represent the 

 cloacal membrane, the fusion of anus and rectum corresponding 

 to the white line in this situation. 



Congenital strictures of the rectum sometimes assume a 



