chap, xvi.j THE ABDOMINAL PARIETES. 295 



In some cases a fistula is found at the navel that 

 discharges urine. This is due to a patent urachus. 

 The urinary bladder is formed by a dilatation of the 

 stalk of the allantois. The part below this dilatation 

 becomes the first part of the urethra, that above 

 becomes the urachus. In one instance of patent 

 urachus the abnormal opening was one inch in diameter. 

 The patient, a man aged 40, had a stone, which was 

 extracted by passing the finger into the bladder through 

 the opening at the umbilicus. 



Sometimes a fistula discharging fseces is met with 

 at the navel This depends upon the persistence of the 

 vitello-intestinal duct, a duct that at one time connects 

 the rudimentary intestine with the yolk sac, and that 

 generally disappears without leaving any trace. The 

 persistent duct, when it occurs, is known as Meckel's 

 diverticulum, and springs from the ileum from one 

 to four feet above the ileo-csecal valve. 



The position of the transverse intersections of the 

 rectus muscle should be borne in mind. They 

 adhere to the anterior layer of the rectus sheath, 

 but not to the posterior. They are able, therefore, 

 in some extent to limit suppurative collections and 

 haemorrhages beneath the sheath on its anterior 

 aspect. This muscle is often the seat of one form of 

 " phantom tumour." These tumours are mostly met 

 with in the hysterical and hypochondriac, and when 

 associated with some vague abdominal symptoms are 

 apt to mislead. They are due to a partial contraction 

 of the muscle, usually to a part between two inter- 

 sections, and are said to be more common in the left 

 rectus. When the fibres of the muscle are contracted 

 the " tumour " is obvious, but when they relax it 

 disappears. Other phantom tumours depend upon 

 irregular contraction of the other abdominal muscles 

 associated with flatulent or faeculent distension of the 

 bowel In great distension of the abdomen the fibres 



