The Tunica Vaginalis

The tunica vaginalis is a somewhat pyriform serous sac which extends from the internal inguinal ring through the inguinal canal to the bottom of the scrotum. Like the abdominal peritoneum, of which it is an evagination, it consists of two layers—parietal and visceral. The parietal layer, or tunica vaginalis communis (s. reflexa), lines the scrotum below; its narrow, tubular part lies in the inguinal canal and is directly continuous with the parietal peritoneum of the abdomen at the internal inguinal ring. The cavity of the tunica vaginalis (Cavum vaginale) is a diverticulum of the general peritoneal cavity, with which it communicates through the vaginal ring (Annulus vaginalis). It contains normally a small quantity of serous fluid. The parietal layer is reflected from the posterior wall of the inguinal canal around the structures of the cord, forming the mesorchium, a fold analogous to the mesentery of the intestine. The visceral layer, or tunica vaginalis propria, covers the spermatic cord, testicle, and epididymis.

The external cremaster muscle (M. cremaster externus) lies on the outer and posterior part of the tunic, to the scrotal part of which it is attached.

Confusion has arisen from the use of the term internal abdominal or inguinal ring in two senses. The term is used to designate the upper or abdominal opening of the inguinal canal, but it is also applied to the upper opening of the cavity of the tunica vaginalis. It should only be applied to the abdominal opening of the canal, the subperitoneal ring. The peritoneal ring at which the cavity of the tunica vaginalis opens into the general peritoneal sac is distinguished by the name vaginal ring. It is placed about four or five inches (ca. 10 to 12 cm.) from the linea alba, and about two or three inches (ca. 6 to 8 cm.) in front of the ilio-pectineal eminence. In stallions it will usually admit the end of the finger readily, but it may be abnormally large and allow a loop of bowel to enter the cavity of the tunica vaginalis. In the gelding it is smaller and sometimes partially occluded. In man the cavity is almost always obliterated early, except in its scrotal portion, thus abolishing the vaginal ring.