PRACTICAL CONSIDERATIONS : ABDOMINAL HERNIA. 1769 



testis, that it may be described here. It derives its name from the protrusion from 

 the sac of an inguinal hernia (usually of the incomplete variety) of a pouch or 

 diverticulum which insinuates itself into or between the separate layers of the ab- 

 dominal wall, as (a) between the peritoneum and transversalis fascia (^ properitoneal 

 hernia) ; ((^) between that fascia and the transversalis muscle, or among the fibres 

 of the internal oblique, or between the internal and external oblique muscles, or 

 sometimes — the transversalis and internal oblique having been pushed aside, as in the 

 descent of an ordinary acquired ysx^xixwdX hernia {vide infra) — between the transver- 

 salis fascia and the external oblique muscle or aponeurosis {interstitial hernia) ; {c) 

 between the external oblique aponeurosis and the skin {superficial inguinal hernia) 

 (Sultan). 



While the exact mechanism of the formation of these herniae is still unknown, 

 and the various conflicting theories — although of great anatomical interest — cannot 

 here be set forth, it is perhaps safe to say that the following facts have a direct bear- 

 ing upon the question : (a) a hernia, like other swellings, enlarges in the direction 

 of least resistance ; {b) the preponderance of the association of these interparietal 

 herniae with incomplete inguinal herniae and with retained testis, in neither of which 

 cases have the external ring and the scrotum undergone dilatation, may be due to a 

 lesser resistance in the course of the diverticulum than at the external ring ; {c) they 

 are also often associated with imperfections of the abdominal wall, correlated with 

 the anomalies of the testicle, because, as Macready says, when that organ is defective 

 it is very probable that the parts through which it passes and with which it is so in- 

 timately associated will likewise be deficient. 



The mechanism of formation of the so-called acquired oblique inguinal hernia — 

 the most frequent and therefore the most important of all forms of hernia — will now 

 readily be understood. Because of the anatomical conditions above enumerated 

 (page 1763), and in the presence of one or more of the etiological factors, the peri- 

 toneum covering the internal ring yields to the pressure of the viscera (usually a 

 portion of the small intestine) and, together with the latter, passes through the in- 

 ternal ring above the cord, the component structures of which, with the artery to the 

 vas deferens, the cremasteric artery, the genital branch of the genito-crural nerve, 

 and the inguinal branch of the ilio-inguinal nerve, are close to the lower margin 

 of the ring. After entering the canal it meets with less resistance, and, aided by 

 gravity and sometimes by prolapse of the mesentery, — a loosening or slipping down 

 of its vertebral attachment, — which slightly increases the weight of the intestines 

 that must be borne by the abdominal wall, descends until it reaches a point at which 

 the resistance is greater than the forces that are carrying it downward. Its descent 

 has been thought to be aided by the weight of masses of fat (subserous lipomata) 

 sometimes found in the extraperitoneal connective tissue that precedes the sac and 

 forms one of the coverings of nearly all abdominal herniae, but this is more than 

 doubtful. The most frequent point of arrest is at the lower part of the canal, where 

 the rigid, non-elastic pillars of the external ring, strengthened by the intercolumnar 

 fibres, often closely embrace the cord, and where the course of the hernia changes 

 slightly in direction. Until it emerges from the external ring it is known as an in- 

 complete heriiia (bubonocele). It is obvious that, with the exception of a few con- 

 genital herniae, every inguinal hernia must at some time have been incomplete. After 

 emerging from the external ring it is known as a complete her^iia and usually enters 

 the scrotum. It then meets with but little resistance until it reaches the level of the 

 upper end of the testicle, where it may be again arrested — often permanently — by 

 the close connection of the coverings of the cord to the tunica vaginalis, or it may 

 descend quite to the bottom of the scrotum {scrotal hernia). It lies throughout its 

 course in front of the spermatic cord. 



In females the corresponding hernia follows the round ligament through the 

 inguinal canal and appears in the labium majus {labial hernia). 



As the peritoneal sac and its contents follow this course from the abdominal 

 cavity downward, they are covered by various structures that represent portions of 

 the different layers of the abdominal wall, modified in character, however, at the time 

 of the descent of the testis and designated by new names. The clinical importance 

 of this list of ' ' coverings' ' has been greatly exaggerated, but they have a certain 



