Part 62

The bladder is covered by peritoneum and is held in place by its neck and by three folds of the peritoneum. One of these passes from its ventral wall to the linea alba and is the =suspensory= ligament. Two others pass one from each side of the bladder to the dorsal body wall at the sides of the rectum. They are the =lateral= ligaments of the bladder. They form the walls of a partly isolated peritoneal pocket into which the rectum passes; this pocket opens craniad into the peritoneal cavity. The wall of the bladder is composed of an internal epithelium, a layer of plain muscle-fibre bundles which cross one another in various directions, and the external peritoneal layer.

SUPRARENAL BODIES. GLANDULÆ SUPRARENALES.--The suprarenal bodies are two ovoid bodies about a centimeter in the longest diameter, lying craniomediad of the kidneys, but usually not touching them. In a fresh condition they are of a pinkish or yellow color. They are usually imbedded in fat and are covered by peritoneum on their ventral surface. They have no duct and are of uncertain function.

2. The Genital Organs.

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:

1. The =scrotum= (the integument).

2. =Cremasteric fascia= (subcutaneous fascia).

3. The =levator scroti muscle= (subcutaneous muscle-layer) (Fig. 113, j).

4. =Tunica vaginalis communis= (transversalis fascia).

5. =Tunica vaginalis propria= (peritoneum).

The tunica vaginalis communis is inseparably united with the parietal layer of the tunica vaginalis propria. Where the spermatic cord passes from the abdominal wall to the scrotum it is covered by integument and cremasteric fascia on its ventral surface only, but is entirely surrounded by the tunica vaginalis propria and tunica vaginalis communis. The canal by which the spermatic cord passes through the body wall is known as the =inguinal canal=. The end by which it opens into the abdominal cavity is the =internal inguinal ring=, and the opposite end is called the =external inguinal ring=.

The =internal inguinal ring= is merely the point of connection between the proximal tubular portion of the tunica vaginalis propria and the abdominal cavity. It is circular, and is situated close against the lateral side of the lateral ligament of the bladder at its middle.

The =external inguinal ring= is an oval opening in the aponeurosis of insertion of the external oblique muscle. The aponeurosis of this muscle ends caudally in a free border along the cranial edge of the pubis, from the ilium to the pubic tubercle. The external ring is just craniad of the end of this aponeurosis.

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.

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).

2. The =membranous= portion (h) extends from the prostate portion to a point between the crura of the penis. This portion is surrounded by the thick compressor urethræ muscle, so that its wall appears much thicker than it really is.

3. The =spongy= portion (pars cavernosa) extends along the ventral side of the penis to its end in the groove between the corpora cavernosa penis. At its beginning is an enlargement formed by the bulbocavernosus muscle. This is known as the =bulbus urethræ=. The walls of the spongy portion are thick and vascular and form the =corpus cavernosum urethræ= or =corpus spongiosum=. At its end the corpus cavernosum urethræ is greatly enlarged and forms the glans penis (m).

GLANDS OF THE URETHRA.--1. The =prostate= (Fig. 111, g) is a bilobed gland lying on the dorsal wall of the urethra and surrounding the ends of the vasa deferentia (c). It opens into the urethra at its beginning by numerous small ducts visible to the naked eye on the inner surface of the urethra.

2. The =bulbourethral= or =Cowper’s glands= (Fig. 111, i).--There are two bulbourethral or Cowper’s glands, one on either side of the bulbus of the urethra between the ischiocavernosus and bulbocavernosus muscles. Each has a covering of muscle-fibres derived from the neighboring bulbocavernosus (Fig. 113, l). Each is said to open by a single duct into the urethra at the root of the penis.