HERNIA 257 



influence of the intra-abdominal pressure, or to the instant 

 rupture of such points when the pressure is suddenly increased. 

 After a pouch of the posterior wall, containing gut, has been 

 protruded into the canal, or after a portion of the peritoneal 

 sac containing gut has been forced through the posterior wall 

 into the canal, the action of the abdominal pressure will tend 

 to force the protrusion along the line of least resistance, 

 which is usually along the canal to the subcutaneous inguinal 

 ring. The coverings of the direct hernia will differ according 

 to whether the hernia has torn the posterior wall or forced it 

 forwards as a covering, and, in the latter case, according to 

 whether the hernia has passed from the medial inguinal pouch, 

 between the inferior epigastric artery and the obliterated part 

 of the umbilical artery, or through the supravesical pouch, at 

 the medial side of the obliterated artery. The coverings of 

 the hernia passing from the medial inguinal pouch will be the 

 same as those of the oblique hernia, except that transversalis 

 fascia will take the place of internal spermatic fascia ; but if 

 the hernia passes from the supravesical pouch, on the medial 

 side of the obliterated part of the umbilical artery, it will push 

 before it the falx inguinalis, it will enter the canal below the 

 upper border of the cremasteric fascia, and it will receive no 

 sheath from the latter fascia ; from within outwards, therefore, 

 its anatomical coverings will be (i) peritoneum, (2) extra- 

 peritoneal fat, (3) transversalis fascia, (4) falx inguinalis, (5) 

 external spermatic fascia, (6) superficial fascia, (7) skin. The 

 student should understand also that whilst it is commonly be- 

 lieved that oblique herniae are usually due to the persistence 

 of a portion of the processus vaginalis, there is no anatomical 

 reason why a new peritoneal sac should not be formed in the 

 region of the lateral inguinal fossa, that is, in the region of 

 the abdominal inguinal ring, as easily as in other regions. If 

 such a pouch were formed it would pass along the line of the 

 canal, its coverings would be similar to those of a hernia 

 which had passed into the upper persisting part of the pro- 

 cessus vaginalis, and its relationship to the tunica vaginalis 

 would depend largely upon the size of the latter sac, that is, 

 upon how much of the lower part of the original processus 

 remained unobliterated, and upon the more anterior or more 

 posterior position of the upper end of the tunica vaginalis. 



Femoral Hernia. This consists in the protrusion of some 

 abdominal contents from the abdominal cavity into the region 



VOL. II 17 



