A. THE MALE GENITAL ORGANS. _External Genital Organs._--The external genital organs are the =scrotum= and =penis=.
The =scrotal sac= or =scrotum= is a pouch of integument which lies ventrad of the anus in the median line against the ischiatic symphysis. It is marked by a median groove which indicates the position of an internal septum dividing its cavity into lateral halves, within each of which is one of the =testes=.
The =penis= (Fig. 111, _l_; Fig. 113, 6; see also page 262) lies ventrad of the scrotal sac. It projects caudad. It is covered by the integument, which projects at its end as a free fold, the =prepuce=. Within the prepuce is the projecting =glans penis= (Fig. 113, 7). It is conical and bears on the ventral side of its free end the opening of the =urethra=, the common urinogenital opening. On the side on which the urethra opens the glans is connected to the prepuce by a fold of integument, the =frenulum=. The surface of the glans is covered with sharp, recurved, horny papillæ.
_The Scrotum and Testes, and the Ducts of the Testes._--The scrotum contains the two =testes=, one in each of its compartments. Each testis lies in a diverticulum of the abdominal cavity, which is lined by an extension of the peritoneum. The testis has the same relation to this peritoneal diverticulum that the intestine has to the abdominal cavity; i.e., it does not lie within the cavity of the diverticulum, but is suspended apparently within it by means of a fold of its wall which acts as a mesentery. The peritoneal diverticulum is called the =tunica vaginalis propria= and consists thus of a =parietal= layer and a =visceral= layer.
The =tunica vaginalis propria= consists of a slender proximal part through which the blood-vessels pass to the testis and the vas deferens from it, and of an expanded distal part in which lies the testis. Only the distal part lies within the scrotum. The blood-vessels and vas deferens are suspended in the narrow part of the tunica vaginalis propria by means of a mesenterial fold similar to that which suspends the testis, and continuous with it. This fold and the blood-vessels and vas deferens contained within it form the =spermatic cord= (Fig. 111, _d_) which passes from the abdomen to the scrotal sac in the narrow part of the tunica vaginalis propria. In the formation of the human tunica vaginalis the various layers of the body wall are carried out by it and form the tunics, or coats of the testis. The one of these coats next the tunica vaginalis propria (which is reckoned as one of the coats) is the =tunica vaginalis communis= (or =fascia propria=) and is formed by the transversalis fascia. Outside of the tunica vaginalis communis is the =cremaster muscle=, an incomplete layer formed from the fibres of the internal oblique muscle. Next is the =cremasteric= (or =intercolumnar=) fascia from the aponeurosis of the external oblique muscle, and outside of this is the integument forming the scrotum. In this integument there is a layer of smooth muscle which is sometimes described as the =tunica dartos=. In the cat the tunica dartos and the cremaster muscle are wanting. The cremaster is replaced by the elevator scroti muscle. The coats of the testis are thus five, as follows: