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received into a hollow in the base of the glans. The skin covering the body of the penis is thin, delicate, and freely movable, and, except near the root of the is free from hairs; on the urethral aspect of the penis the skin is marked by a median raphe, continuous with the raphe of the scrotum. Traced towards the base of the glans, the skin forms a free fold called the præputium, or prepuce, which overlaps the glans to a variable extent. From the deep surface of the prepuce the skin is reflected on to the terminal part of the penis, along a line just proximal to the corona glandis, and is continued over the entire glans to the external urethral orifice. A small median fold, the frenulum præputii, passes to the deep surface of the prepuce from a point immediately below the orificium urethræ externum. The skin covering the glans is firmly attached to the underlying erectile tissue, and here, as well as on the deep surface of the prepuce, it presents some resemblance to mucous membrane.
Sometimes minute sebaceous glands, glandulæ præputiales, are found in very variable numbers on the glans and inner surface of the prepuce; the secretion from these when they are present may help to form the smegma præputii, which tends to collect in the groove between the glans and the prepuce. The main source of the smegma is to be found in the desquamated and broken-down epithelial cells derived from the surface of the glans and prepuce.
At the radix penis, or root, the three component parts of the organ separate from one another (Fig. 1018). The corpora cavernosa penis, diverging from each other laterally, at first become somewhat swollen, and then, gradually tapering, gain a firm, fibrous attachment to the periosteum on the medial surface of the pubic arch. These diverging parts of the corpora cavernosa are called the crura penis, and each is covered by the corresponding ischio-cavernosus muscle. The corpus cavernosum urethræ lying between the crura becomes enlarged, and forms a somewhat spherical mass which receives the name bulbus urethræ. The bulb varies much in size in different individuals, and is attached to the under surface of the fascia inferior of the urogenital diaphragm, against which it rests. The posterior part and under surface of the bulb usually show a median notch or groove-an indication that the bulb is originally composed of two symmetrical portions, which during development have become fused in the median plane. These two portions are termed the hemispheria bulbi urethra, and are best seen in subjects whose tissues have been hardened by intravascular injection. A slightly marked median septum, situated within the bulb tissue, indicates on a deeper plane the line along which fusion has taken place. The canal of the urethra, piercing the fascia inferior of the urogenital diaphragm, enters the bulb obliquely a short distance in front of its posterior extremity (Fig. 1024). Covering the superficial surface of the bulb is the bulbo-cavernosus muscle.
A somewhat triangular band of strong fibrous tissue, called the ligamentum suspensorium penis, is attached to the front of the symphysis pubis, and extends o the fibrous capsule of the penis, with which it becomes continuous (Fig. 1017).
FIG. 1018.-STRUCTURES COMPOSING THE RADIX PENIS.
Structure of the Penis.-Each corpus cavernosum penis is enclosed by a dense white fibrous coat-tunica albuginea corporum cavernosorum, which, fusing with the corresponding coat of the opposite side, forms a median septum penis. The septum is very incomplete, especially near the terminal part of the penis, where it is interrupted by a number of nearly parallel slit-like perforations; hence the term "septum pectiniforme" is often applied to it (Figs. 1019 and 1020). Through these openings the erectile tissue of the corpora cavernosa of opposite sides is continuous.
The fibrous coat contains some elastic fibres, and may be divided into an outer layer of longitudinally directed fibres and an inner layer of circular fibres, some of which latter are continued into the septum. Numerous fibrous strands, called trabecula corporum cavernosorum, proceed from the deep surface of the tunica albuginea, and stretching across the interior of the corpus cavernosum, form a fine sponge-like framework whose interspaces communicate freely with one another, and are filled with blood. These blood-containing spaces lead directly into the veins of the penis, and, like the veins, have a lining of flat endothelial cells. The size of the penis varies with the amount of blood in this cavernous tissue. The structure of the corpus cavernosum urethræ resembles that of the corpora cavernosa penis, but the fibrous coat is much thinner and more elastic, and the trabeculæ are finer (Fig. 1019).
The glans penis is also composed of cavernous tissue which communicates by a rich venous plexus, situated on the ventral aspect of the urethra, with the corpus spongiosum urethræ. No strongly marked tunica albuginea is present, and the erectile tissue is practically bounded by the firmly adherent skin. Surrounding the urethra, which in this part of the penis is represented by a laterally compressed slit-like passage, is a mass of fibro-elastic tissue which forms a kind of median septum within the glans. This septum
Dorsal vein Dorsal artery
FIG. 1019.-TRANSVERSE SECTION THROUGH THE
Corpus cavernosum penis
FIG. 1020.-A LONGITUDINAL SECTION OF THE
is continued backwards to join the sheath of the conical end of the corpora cavernosa, and ventrally it gives attachment to the frenulum of the prepuce. It imperfectly divides the erectile tissue of the glans into right and left portions, which, however, freely communicate dorsally. From the septum, trabeculæ pass out in all directions into the tissue of the glans. Loosely surrounding the corpora cavernosa penis and the corpus cavernosum urethra is a fibrous sheath containing numerous elastic tissue fibres. This sheath is termed the fascia penis, and reaches as far as the base of the glans, where it becomes fixed to the floor of the groove limited by the corona glandis. In its proximal part the sheath gives insertion to many of the fibres of the bulbo-cavernosus and ischio-cavernosus muscles.
Superficial to the fascia penis is a layer of extremely lax areolar tissue, and more superficial still is a prolongation of the tunica dartos of the scrotum, covered by the delicate skin of the penis. Numerous sebaceous glands are present in the skin, especially on the urethral aspect of the penis.
In some mammals, such as the walrus, dog, bear, baboon, etc., a bone called the os penis developed in the septum which intervenes between the corpora cavernosa penis.
Vessels and Nerves of the Penis.-The penis receives its arterial supply from branches of the internal pudendal artery. The erectile tissue of the corpora cavernosa penis is supplied chiefly by the deep arteries of the penis, while that of the corpus cavernosum urethræ receives its arterial supply from the artery to the bulb. Branches of the dorsal artery of the penis piercing the fibrous coat of the corpora cavernosa penis furnish additional twigs to the erectile tissue of these structures. The glans receives its chief blood-supply from branches of the dorsal artery. The small branches of these arteries run in the trabeculae of the erectile tissue, and the capillaries, into which they lead, open directly into the cavernous venous spaces. As they lie in the finer trabecule the smaller branches often present a peculiar twisted appearance. and hence the name arteriæ helicinæ is sometimes applied to them.
The veins with which the cavernous spaces communicate, carry the blood, for the most part, either directly into the pudendal plexus, or into the dorsal vein and so to the pudendal plexus. The dorsal vein of the penis begins in tributaries from the glans and prepuce, and lies in the groove between the corpora cavernosa penis as it ascends to pass beneath the arcuate ligament of the pubis to join the pudendal plexus. On each side of it lies the dorsal artery, and still farther from the median plane lies the dorsal nerve (Fig. 1019).
The lymph-vessels of the penis are arranged in a deep and superficial series, and end in the medial glands of the inguinal group of lymph-glands.
The nerve-supply of the penis is derived from the pudendal nerve and from the hypogastric and pelvic plexuses. The branches of the pudendal are the dorsal nerve of the penis, and branches from the perineal nerves. These supply the cutaneous structures of the penis, while the sympathetic filaments from the hypogastric and pelvic plexuses, which reach the penis through the prostatic nerve plexus, end in the erectile tissue.
The prostata, or prostate, is a partly glandular, partly muscular organ of a dark brown-red colour which surrounds the beginning of the urethra in the male. It lies within the pelvis behind the pubes, and is enclosed by a dense sheath derived from the pelvic fascia. Through the various connexions of this sheath the prostate is firmly fixed within the pelvic cavity. The ejaculatory ducts traverse the prostate in their course downwards and forwards to join the urethra as it
Median umbilical ligament (urachus)
FIG. 1021.-URINARY BLADDER, PROSTATE, AND SEMINAL VESICLES VIEWED FROM THE SILE. Drawn from specimens hardened in situ.
descends through the gland (Fig. 1023). The size of the prostate varies considerably in different individuals, but its transverse, or longest, diameter is usually from one and a quarter to one and a half inches; its antero-posterior diameter about three-quarters of an inch; and its vertical diameter about one and a quarter inches. Superficially the prostate is separated from the bladder by deep wide lateral grooves directed downwards and forwards, and by a narrow posterior groove which is horizontal.
In connexion with the prostate we describe an apex which is directed downwards, a base looking upwards, a posterior, and two lateral surfaces. The general outline of the organ has been often compared with that of a Spanish chestnut. The upper surface, or basis prostatæ, is directed upwards against the inferior aspect of the bladder, in the neighbourhood of its urethral opening. The greater part of this surface is structurally continuous with the bladder wall, only a narrow portion remains free on each side, and forms the lower limit of the deep groove which marks the separation of the bladder and prostate (Fig. 1021). The lateral surfaces of the prostate are convex and prominent, especially in their posterior and upper portions, and rest against the fascia covering the levator ani muscle. They are directed for the most part laterally, downwards, and somewhat forwards, and meet together in front in a rounded anterior border, sometimes called the "anterior surface," or "facies anterior," of the prostate. Posteriorly the prostate presents a flattened somewhat triangular posterior surface, directed backwards and downwards
against the anterior wall of the rectum, from which it is separated by a layer of the pelvic fascia. This flattened facies posterior is separated on each side from the lateral surfaces by a rounded border which, beginning above at the prominent lateral part of the prostate, ends below at the apex of the organ. The apex prostatæ points downwards, and is in relation to the sphincter urethræ membranacea muscle, from which it is separated by the fascia superior of the urogenital diaphragm. From the apex the rounded anterior border, which separates the lateral surfaces, passes upwards in the median plane behind the symphysis pubis and retropubic pad of fat. This border is interrupted in its lower part by the passage of the
When the sheath formed by the pelvic fascia is stripped off the prostate the organ has a more rounded outline, and the surfaces just described are not so clearly defined. The anterior border may now appear to be rather a surface than a border, and the antero-posterior diameter of the whole organ is considerably reduced.
The urethra enters the prostate at a point near the middle of its upper surface, and leaves it at a point situated on its anterior border, just above and in front of the apex. As it descends, the urethra describes a curve which is concave forwards, and in median section it is seen to lie, on the whole, nearer to the posterior surface than to the anterior border of the gland.
The ejaculatory ducts, entering a slit-like interval, or hilum, situated just in front of the border which separates the base from the posterior surface of the prostate, run downwards, medially, and forwards, to open into the prostatic portion of the urethra very close to one another. The somewhat wedge-shaped portion of the prostate, which lies between these ducts and the posterior aspect of the urethra, receives the name of lobus medius (Fig. 1023). The base of this middle lobe projects upwards against the bladder, and is continuous with the part of the bladder wall lying immediately behind the urethral orifice. When hypertrophied, as it often is in deferens old people, the middle lobe of the prostate may cause a considerable elevation in the cavity of the bladder, to which the term uvula vesicæ is applied. This elevation possesses considerable surgical interest (p. 1277)
The rest of the prostate is described as being composed of two large lateral lobes, which are, however, not.marked off from one another superficially.
In front of the prostate, between it and the pubis, is a rich venous plexus-plexus pudendalis in which the dorsal vein of the penis terminates. This plexus is continued backwards, on each side, round the lateral aspect of the prostate, and joins the large thin-walled veins which are collected for the most part in the deep sulcus between the bladder wall and the prostate, and form the prostatico-vesical plexus. Most of the veins forming this plexus lie partly within and partly outside the dense fibrous sheath of the prostate, which is derived from the visceral pelvic fascia (Figs. 1023 and 1024).
Fibrous Sheath of the Prostate. The sheath of the prostate is formed by the visceral pelvic fascia, and closely invests the gland on its lateral and posterior aspects. Inferiorly at the apex of the prostate the sheath becomes continuous with the fascia superior of the urogenital diaphragm, which lies above the sphincter urethræ membranacea muscle, and is attached to the pubic arch. In front two thickened bands pass forwards from the anterior aspect of the sheath, one on each side of the median plane, to reach the back of the lower part of the pubis, where
Drawn from a specimen hardened in situ. The lateral surfaces of the prostate are seen one on each side of the urethra and in front of the posterior surface.
they are attached to the periosteum. These constitute the pubo-prostatic ligaments, and contain smooth muscle fibres, as well as dense connective tissue. Some of the muscle fibres in connexion with the pubo-prostatic ligaments, passing upwards as well as backwards, gain the bladder wall, and are spoken of as the pubo-vesical muscles. Below the pubo-prostatic ligaments the medial edges of the levatores ani muscles pass medially and almost meet together in front of the apex of the prostate. When followed backwards, the medial edges of these muscles are seen to closely embrace the apex of the prostate. This layer forms a part of the wall of the retro-pubic space which lies in front of the prostate and below the bladder (Fig. 1024).
Between the pubo-prostatic ligaments there is a shallow fossa, or depression, the floor of which is formed by a thin layer of fascia connecting the anterior aspect of the sheath of the prostate with the back of the pubis. On each side of the body the lateral aspect of the sheath of the prostate is continuous with the strong fascia which covers the pelvic surface of the levator ani muscle. When the fibrous sheath of the prostate is traced upwards beyond the level of the upper margin of the gland it becomes thinned out and joins the fascial covering of the bladder. Posteriorly the
Prostatic ducts open here
Ejaculatory ducts Lobules of gland
FIG. 1023, A and B.-HORIZONTAL SECTIONS THROUGH THE PROSTATE. Section A lies at a higher level than B.
upward prolongation of the sheath is continuous with the fascial layers which enclose the ampullæ of the ductus deferentes and the seminal vesicles, and it is adherent to the peritoneum of the recto-vesical pouch. In this position it is often spoken of as the recto-vesical fascia.
Structure of the Prostate.-Beneath the fibrous sheath of the gland the superficial part of the prostate is seen to be largely composed of matted interlacing bundles of smooth muscle and connective tissue fibres, which form a kind of capsule for the deeper parts of the organ. This layer, or capsule of the prostate, is not sharply defined, but from its deep aspect fibrous and muscular strands pass inwards, converging towards the posterior wall of the urethra, to become continuous with the mass of smooth muscular tissue which surrounds this canal as it traverses the prostate. These somewhat radially arranged strands divide the prostate into a number of incompletely defined lobules, of which there appear to be about fifty. The yellowish-coloured glandular tissue, or corpus glandulare, which forms the lobules is composed of minute, slightly branched tubules, the walls of which in certain places show numerous saccular dilatations. In the upper portion of the gland the tubules are slightly dilated and shorter than in the lower part, where they are longer and more convoluted. The glandular tubules lead into the minute prostatic ducts, which open into the urethral canal as it traverses the prostate. The ductus prostatici number about twenty or thirty, and open for the most part into a groove on each side of the median elevation, or crista urethralis, in the posterior wall of the urethra (Fig. 1023 A).
The bulk of the glandular tissue is situated at the sides of and behind the urethra. In front of the upper part of the prostatic portion of the urethra there is a mass of