Penile Anatomy

The penis, whose anterior or foremost portion is between 9 and 10 cm. long, and projects or, rather, hangs loosely, possesses an invisible posterior or hind portion, the root, which runs beneath the perineal skin and the junction of the scrotum, hidden to the sight but easily felt by the fingers.

The portion of the shaft of the penis, which is turned upwards and outwards, lies below the symphysis in the pubic arch, and attached by broad and firm muscles to the bony framework of the pelvis, which gives the organ secure anchorage.

The main portion of the penis is composed of hollow or cavernous tissue (corpora cavernosa), that is, of a spongy network of blood-vessels, which become stretched and tense when congested. There are two such corpora cavernosa here.

The male member contains one urethral and two penile corpora cavernosa. The former is usually known as the corpus spongiosum.

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They run parallel, but are closely connected, and may be regarded as one organ, which forms the greater part of the member when loosely suspended, i.e. Its dorsal part (namely, that portion in the passive non-erected penis which faces forwards, and away from the scrotum). The hind portion, which has similar shading, attaches the organ to the symphysis pubis.

The urethral corpus is in its longest (medial) section, a comparatively narrow column, surrounding the urethra. In the loosely hanging (non-erect) penis it is the portion turned towards the scrotum.

Behind it becomes much more massive, and forms the aforesaid root of the organ, which can be felt under the scrotum, and is known as the bulbus urethra (bulb of the urethra).

Towards the extremity of the organ the corpus urethra suddenly expands and forms the tip or gland of the penis, which extends beyond the penile corpus cavernosum and occupies the entire extremity.

The cavity here is called corpus cavernosum glandis. The urethral, penile, and glandular cavities are all closely interconnected, and form a structural unity, which answers as one organ to stimulation.

Whether the stimulation proceeds from the central nervous system (brain), or is local and peripheral, the effect is the same. The erection of the member, that is, its enlargement, hardening and change of position through the increased flow of blood into the veins of the corpora cavernosa till they are congested to their fullest extent.

The corpora cavernosa are encased in elastic fibers and tendons, which possess enough elasticity and pliancy to make a surprising expansion of the organ possible, but, on the other hand, to give the vascular tissue substance and support and prevent rupture of the distended blood-vessels.

The skin of the male organ is almost devoid of hair; it is thin, sensitive, elastic and dilatable. It sheaths the organs without an intermediate layer of adipose tissue (fat), but loosely, so that it can be slipped to and fro like a glove.

At the extremity it forms a double fold, so that instead of being firmly joined to the glans penis it is attached 2 or 3 min. behind the rim, at the upper, front angle of the shaft. This double fold of skin is the prepuce, or foreskin. In young children and immature boys it extends beyond the glans and covers it.

In adults the glans penis is generally just visible as it protrudes in the aperture of the foreskin. This aperture is normally wide enough, and the foreskin sufficiently elastic, to be easily pushed back.

 Then the exact shape of the glans, hitherto indistinct, is revealed as a blunted or truncated cone, which is longer and thicker at the posterior than at the scrotal side of the penis. In consequence, the slightly prominent hind rim of the top, the corona glandis, is not circular, but an oval, whose plane is at an angle to the axis of the penis itself.

Thus the preputial sack or sack of the foreskin is deeper and roomier on the dorsal side of the penis than on the scrotal side.

On the scrotal side in the centre is a tiny strip, which connects gland and prepuce and prevents too deep an exposure of the gland. This is called the Frenulum preputi.

The glans penis is covered by a continuation of the inner preputial lining, i.e. a membrane which does not resemble the epidermis. At the edge of the ostium uretha this merges into the mucous membrane.

The skin of the glans has very sensitive neurons of different types, bound together by numerous reticulations, so that a close network of the most delicate sensory apparatus is constructed, and is peculiarly adapted to receive even the slightest mechanical stimuli and transmit them to the brain, which feels them - if they are not so violent as to cause acute pain - as specific sexual pleasure.

The exact area of maximum sensibility for sexual pleasure is the lower surface of the glans (especially the band or frenulum), which even surpasses the upper (posterior) rim or corona - also a highly charged and susceptible nerve cluster.

The foreskin is also rich in neurons, which serve the same purpose, as is also the whole skin of the penis, though the sensation attained here is less acute than at the extremity.

Mechanical stimulation of these neurons causes a reflex congestion of the corpora cavernosa, and the organ becomes erect. This may also and equally be caused directly from the brain through psychological stimulation. Indeed, the latter type of stimulus is probably the more frequent; direct mechanical excitation comes into play after the erection has begun.

The process of erection transforms the soft, small, drooping penis, which in its passive state could not possibly perform the sexual act, into a stiff, firm, yet elastic instrument, perfectly adapted for pouring out its seminal liquid into the furthest recesses of the female parts, for in full erection against the man's abdomen it generally lies at an angle and with a slight backward curve, which exactly fit into the normal vaginal angle and curve forward.

Moreover, in normal cases, the length and circumference of the erect male member completely fill the vagina (which is distended lengthwise in coitus) if penetration is not quite up to the "hilt" or root. Nevertheless, there are considerable individual differences here.

The length of the visible shaft of the penis in erection is between 14 and 16 cm; its circumference in the middle 12 cm.

The urethra or urinary passage or duct is the long, curved conduit which passes from the bladder and cuts through the penis. Its uppermost portion, i.e. that directly in touch with the bladder, serves solely for the passage of urine.

But from the point where the seminal ducts (vas deferens) join it on either side it also receives and conducts the spermatic secretions.

The urethra may be divided into three portions, according to the bodily areas through which it passes.

The first, or uppermost, is within the pelvis; when the man stands upright on his feet, the direction of this part of the urethra is almost vertical, and directed downwards. It is mainly surrounded by the prostate gland and separated from the bladder by a powerful sphincter muscle.

Below the symphysis, between the prostate and the corpora cavernosa, the urethra changes its direction, and passes through the muscular tissue of the pelvic floor and enters its perineal portion.

This second urethral region, which lies beneath the pelvic floor, ends in the roots of the penis, and has the same horizontal direction and slight upward slope. At its second, downward curve, where the loosely hanging exterior portion of the penis begins, there begins also its third (or penile) region.

The second and third portions are shown in the diagram, within the corpora cavernosa. In medical practice they are together termed the anterior (or front) urethra, while the short, vertical portion within the pelvis is called the posterior (or hind) urethra.

The length of the anterior urethra, when the penis is in its normal slack and pendant state, is about 15 cm. When the penis rises in erection, it lifts the urethra, whose slight downwards curve can be obviated at other times by lifting it with the hand, as in urination.

The urethra stretches itself elastically when the penis becomes erect, and its direction becomes vertical, though still with a slight curve. The urethra expands when passing through the glans, or penile tip, and at once contracts at its external orifice into a tiny vertical slit, its narrowest portion throughout the whole of its length.

In the anterior urethra are a good many very small glands, which, together with Cowper's glands, secrete a small amount of transparent, thin, alkaline and very slippery fluid, instrumental in making the glans slippery and facilitating its insertion into the vagina.

The secretions of Cowper's glands help to make the urethra more suited to receive and transmit the semen, for they counteract the effects of the distinctly acid urine, by their own alkalinity.

This latter function may be less important than lubrication, however, for there can only be very slight traces of urine in the urethra during the passage of a much greater amount of semen, and this passage is extraordinarily rapid.

The mucus secretion of Cowper's and the urethral accessory glands, may appear after the local excitation and erection of the male organ, and thus form, as it were, a second stage in the process of preparation for union. Or it may appear while the member is still slack, or at least not in full tension.

The latter is especially the case if sexual excitement is produced through solely psychic impressions such as thoughts, books, pictures, without contact with a woman, or if foreplay is extended.

Inexperienced young men, who are anxious about their mental and physical health and their virile potency, may mistake this normal lubrication for loss of semen. It is nothing of the kind. It is a distinct process, which prepares the penis for coitus and at the same time expresses the soul's desires.

The testes or testicles (singular, testis) are two oval bodies, enclosed in a sack or bag, the scrotum. The left testicle is generally slightly the lower of the two, and the whole structure has thus an asymmetrical look.

In normal proportions, the centre of the scrotum should reach lower down than the tip of the slack penis. The skin of the scrotum is darkish, and thickly covered with hair; there is no adipose (fatty) layer.

Under the skin are thick layers of smooth (involuntary) muscular tissue which contract in response to various stimuli (e.g. extreme cold) and turn the loose scrotal pouch into a firm one, with a somewhat wrinkled surface.

As this aspect is considered the more attractive, artists, especially in classic antiquity, have always chosen to perpetuate it in their marble statues.

The scrotum is divided by a partition, in which the sinews are conjoined, and each division contains one testicle and one epididymis. The partition is continued externally in a sort of seam or fold, which runs backward into the perineum, and forward on to the lower surface of the penis.

Testicle and penis are close together, and functionally inter-dependent. In the testicles the spermatozoa are formed; through the penis they are transferred from the body.

But in order to pass into the penis and achieve ejaculation, the spermatozoa have to go a long way round. This is due to biological evolution, for the testicles were originally contained in the pelvic cavity, and only descended into the scrotum at a comparatively recent stage.

In many species of animals this process is repeated in the individual, for the testicles normally repose within the abdomen, and only descend into the scrotum and become visible during the breeding season (time of sexual activity, or rut).

There are certain conditions and peculiarities of structure among men which recall this ancient stage of evolution (rupture, hernia, cryptorchism).

The path taken by the testicle in its primeval descent from abdomen to scrotum is traced for us still in the convolutions of the spermatic cord. This consists of the ducts (vasa deferentia), with a network of nerves and blood-vessels, and runs through the hollow of the groin, above the symphysis, down to the back of the testicle.

Testicle, epididymis and cord are - on either side - surrounded with muscles and membranes corresponding to the layers of the abdominal wall. Parallel are clusters of sinews which can lift the testicles (the cremaster muscle).

This lifting occurs together with a contraction of the scrotum. It can be exemplified, by a typical reflex action, if the inner surface of one thigh is rubbed with short strokes. The testicle on that side will visibly rise.