234 ABDOMEN 



prominent part of this bulging. The fibrous cord is the remains 

 of the tube of peritoneum which, in the foetus, connected the 

 serous investment of the testis (the tunica vaginalis) with the 

 general peritoneal lining of the abdomen. In some cases it may 

 be traced as far as the testis, but more commonly it extends 

 down the cord only for a short distance ; indeed, it is frequently 

 absent. 



To obtain a proper conception of the fibrous thread, it is 

 necessary that the student should understand that neither the 

 testis nor the tunica vaginalis are developed in the scrotum. 

 In the early months of foetal life the rudimentary scrotum 

 contains neither tunica vaginalis nor testis ; the testis lies 

 on the posterior wall of the abdomen, projecting forwards 

 into the great serous cavity of the abdomen, which is called 

 the peritoneal cavity. The wall of the peritoneal cavity is 

 formed by a membrane called the peritoneum, and the inner 

 surface of the membrane is lined with a layer of flat epithelium 

 peritoneal epithelium. The peritoneum which is in con- 

 tact, externally, with the wall of the abdomen is called the 

 parietal peritoneum but here and there the posterior wall of 

 the peritoneal sac is invaginated by one or other of the 

 abdominal viscera. When the invaginating viscus carries 

 forward more peritoneum than is necessary to cover its sur- 

 faces, the excess of peritoneum forms a fold which connects 

 the viscus with the posterior wall of the abdomen ; such folds 

 are called mesenteries and they connect the peritoneum cover- 

 ing the invaginating viscus, which is termed the visceral peri- 

 toneum, with the parietal peritoneum lining the inner surface 

 of the abdominal wall. The testis is developed in the lumbar 

 region ; and it projects forwards into the peritoneal cavity, 

 covered with a layer of epithelium which is continuous with 

 the peritoneal epithelium. It also invaginates a portion of 

 the wall of the peritoneal sac and so produces a mesentery 

 connecting the testis and the epithelium which covers its 

 surface with the parietal peritoneum ; this mesentery is called 

 the mesorchium. 



The testis and its mesorchium gradually descend in the 

 wall of the peritoneal sac to the inguinal region ; and, at the 

 same time, a diverticulum of peritoneum, the processus vaginalis, 

 is projected through the inguinal portion of the abdominal 

 wall into the scrotum, producing by its passage the inguinal 

 canal, and prolonging the cavity of the peritoneum into the 

 scrotum. During the latter part of the seventh and the 



