The inguinal canal between these rings lies along the lateral border of the rectus muscle. It is one to one and a half centimeters long. Its medial wall rests on the rectus muscle; its dorsal wall on the fat contained within the lateral ligament of the bladder. The lateral and ventral walls lie on the transversus muscle proximally, on the internal oblique near the distal end. The wall itself is composed of tunica vaginalis propria and communis. As it passes within the caudal border of the internal oblique muscle it receives some aponeurotic fibres from it. A thin aponeurosis is also continued from the border of the external ring onto the tunica vaginalis propria.

[Fig. 110].—Testis.

a, testis; b, caput epididymis; c, epididymis; d, cauda epididymis; e, vas deferens; f, spermatic cord.

The testes ([Fig. 110]) are the organs which produce the spermatozoa. They lie one in each compartment of the scrotal sac, enveloped in the membranes or tunics [described] when treating of the scrotum. Each is attached to the dorsal wall of its peritoneal pouch by a mesenteric fold. The testis is surrounded by the visceral layer of the tunica vaginalis propria, and within this, by a dense fibrous covering, the tunica albuginea, which sends septa into its interior. Within the fibrous covering it is made up of numerous coils of seminiferous tubules which are readily seen by the naked eye.

The epididymis ([Fig. 110], c) is the beginning of the efferent duct of the testis. It appears as a flat band with a broad rounded end which lies on the medial surface of the testis at its cranial end (b). From this point it passes about the cranial end of the testis from its medial to its lateral surface, forming thus a semicircle with the convexity ventrad. Thence it passes as a narrower band (c) along the dorsal side of the testis, laterad of the suspending mesentery, to the caudal end of the testis (d). At the caudal end of the testis it is enlarged, passes from its lateral to its medial surface, and turns at the same time craniad to become continuous with the vas deferens (e).

The enlarged cranial end is the caput epididymis (b); the enlarged caudal end the cauda epididymis (d). The whole epididymis is encased in a tough fibrous covering similar to that of the testis. The fibrous covering (albuginea) of the testis and that of the epididymis are connected by fibrous tissue. Within the fibrous covering the head of the epididymis is made up of tubules which pass from the testis into its end: these are the vasa efferentia testis. The vasa efferentia unite within the caput into a single vessel which passes in a very tortuous course to the cauda. Its numerous windings form the cauda, from the end of which it passes craniad as the vas deferens (e).

The vas deferens ([Fig. 110], e; [Fig. 111], c) is a slender tube much convoluted at its beginning. It passes from the cauda epididymis (d) along the mesenterial fold of the testis on its medial side, to the spermatic cord ([Fig. 111], d). It leaves the spermatic cord at the internal inguinal ring and, curving over the ureter ([Fig. 111], b), bends craniad and approaches the vas deferens of the opposite side dorsad of the neck of the bladder ([Fig. 111], f). The two vasa deferentia pass caudad together as far as the cranial border of the pubis. There they enter the prostate gland (g), pierce the dorsal wall of the neck of the bladder, and open close together on the inner surface. The two openings are separated by a slight elevation, the veru montanum.

The Urethra ([Fig. 111], h).—The urethra is the common urinogenital duct which is formed by the union of the neck of the bladder (f) and the vasa deferentia (c) dorsad of the cranial border of the pubis. It extends thence to the end of the penis. It is divided into three portions.

1. The prostate portion is the commencement of the urethra; it is surrounded by the prostate gland (g).