This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
There are two forms of inguinal hernia, the congenital and the acquired. These are subdivided into several varieties which can only be understood by having a knowledge of the development and construction of the parts involved.
The testicle originates in the lumbar region inside of the abdomen about the third month. It is behind the peritoneum and has a fold of peritoneum, the plica vascularis, passing upward from it, containing the spermatic artery and veins, and a fold passing downward to the inguinal region and into the scrotum called the gubernaculum. By the fifth or sixth month the testicle has reached the abdominal wall at the internal ring, after which it enters the inguinal canal to pass into the scrotum in the eighth or ninth month of fetal life. A process of peritoneum - the vaginal process - precedes the passage of the testicle into the scrotum. The neck of the vaginal process is called the funicular process. Soon after birth the vaginal process becomes occluded, first at the internal ring, and thence downward until the testicle is reached, where the unobliterated portion forms the tunica vaginalis testis.
There are several forms of congenital herniae. They are so named, not because they exist from birth, but because they are caused by developmental defects which exist at birth (Fig. 394).
The various kinds of herniae due to developmental defects have been named as follows: vaginal - or congenital - funicular, encysted, and infantile.
Vaginal hernia into the processus vaginalis, commonly known as congenital hernia, is where the vaginal process remains entirely open and the intestine passes down to the testicle. In this form the testicle is found protruding into and at the bottom of the hernial sac. Funicular Hernia. - In this form the vaginal process is occluded just above the testicle, but the funicular process above remains open and the intestine descends into it. Encysted Hernia. - Here the vaginal process is occluded at the internal ring only, the remainder forming a continuous sac below containing the testicle. When the intestine descends it pushes this septum, like the finger of a glove, down into the cavity containing the testicle. In operation, two serous layers would be incised, within one of which is the testicle and within the other the intestine. Infantile Hernia. - In this form also the vaginal process is occluded only at the internal ring. As the intestine descends it forms a sac posterior to the point of occlusion and vaginal process. Thus in operation three serous layers are cut through in exposing the intestine and the sac is posterior to the testicle.
Fig. 395. - Parts concerned in inguinal hernia; the external abdominal ring.