The instant a tongue-tip touches it, the man’s expression breaks. That scene is drawn again and again in adult video and in erotic manga. Gaze and voice concentrate there, the region of the male body that “reacts” most deftly.

Kitou (亀頭, literally “turtle head”; Latin glans penis; English glans) is the anatomical term for the bulbous distal end of the penis. It is a conical or bell-shaped structure formed by the expansion of the distal end of the corpus spongiosum (corpus spongiosum penis); its surface is covered in mucosal epithelium, and sensory nerve endings are densely distributed there. It is positioned as a principal male erogenous zone.

Overview

The glans is demarcated from the penile shaft by the coronal sulcus (sulcus coronarius), and in the uncircumcised is covered by the foreskin (preputium). At penile erection from sexual arousal, the engorgement of the corpus spongiosum tenses the mucosa of the glans surface and heightens the sensitivity of the nerve endings. It therefore functions as a principal target of stimulation in sexual acts.

In Japanese colloquial usage kitou serves as the standard medical term, while trade and slang terms such as karikubi (“goose-neck”), kari-kubi, and kari (“goose”) coexist. These are figurative names from the resemblance of the rim around the coronal sulcus at the glans base to a goose’s neck, traditional expressions traceable to Edo-period descriptions of manners. The word kitou itself is a figurative naming likening the roundness of the bulb and the step of the coronal sulcus to the in-and-out of a turtle’s head, a term used since premodern times in the lineage of traditional Sino-Japanese medicine and herbology. Naming organs after animal forms is widespread in East Asian traditional medicine, and the layering of figures, turtle, goose, matsutake-mushroom, shows that the region has long been an object of observation and naming. While the modern standard name kitou took root as the medical term, the slang cluster with the stem kari retains its own vitality as a working term of the sex trade and adult expression.

Anatomical structure

The structure of the glans consists of the internal corpus spongiosum tissue and the mucosal epithelial layer covering its surface. The spongiosum is continuous with the corpus spongiosum of the penile shaft, swelling at erection by the filling of its cavernous spaces with blood. Unlike the corpora cavernosa, however, its tunica albuginea is thin and the hardness at erection is kept lower, so it serves a cushioning function against the physical contact of sexual acts.

The surface mucosa is stratified squamous epithelium, non-keratinised in the uncircumcised and, in the circumcised, mildly keratinised as an adaptation to friction and drying. Sensory nerve endings (Meissner corpuscles, Ruffini corpuscles, free nerve endings) are densely distributed in the superficial mucosa, concentrated especially at the coronal sulcus and the frenulum. On the ventral side at the glans base runs the frenulum of the prepuce (frenulum preputii), a thin fold-like structure fixing the foreskin to the penile shaft and, as one of the concentration points of sensory endings, showing high sexual sensitivity. The region called “ura-suji” (back-tendon) in Japanese slang corresponds roughly to this frenular region.

At the apex of the glans the external urethral orifice (ostium urethrae externum) opens as a longitudinal slit, through which urine and semen are discharged. Its shape and position vary individually, and variants from the developmental process of urethral formation, such as ventrally displaced openings (hypospadias), are known. An important associated structure is the bulbourethral (Cowper’s) gland opening into the urethra; the alkaline mucus secreted from it at sexual arousal exudes at the orifice as so-called pre-ejaculatory fluid, neutralising the acidic environment within the urethra before ejaculation and helping the passage of sperm. In adult expression this secretion is often depicted as a visual index of the degree of arousal.

Physiology and position as an erogenous zone

The sensory nerve density of the glans surface is one of the highest regions of the male body. The dorsal nerve of the penis (nervus dorsalis penis, a branch of the pudendal nerve) supplies the glans surface in a net, showing keen response to mechanical, thermal, and frictional stimulation. Across the phases of arousal: in the excitement phase the glans swells with spongiosal engorgement and its sensory threshold lowers; in the plateau phase engorgement around the coronal sulcus becomes marked and the colour deepens to dark red, while bulbourethral mucus exudes at the orifice; at ejaculation, rhythmic contraction of the corpus spongiosum drives semen out through the urethra.

Glans sensitivity varies greatly between individuals. Sensory comparison between the circumcised and the uncircumcised has been a long-standing research theme. The measurement study by Sorrells et al. (2007) found the highest tactile sensitivity at the inner foreskin and frenulum of the uncircumcised, and reported the glans of the uncircumcised to be somewhat more sensitive than that of the circumcised. On the other hand, other studies hold that circumcision does not markedly impair sexual sensation, and the academic debate continues. citation needed

The relation to phimosis cannot be ignored in discussing glans physiology. In true phimosis, where the glans is permanently covered by foreskin, the surface mucosa, less exposed to friction and drying, remains non-keratinised, and may show strong hypersensitivity when first exposed. Conversely, a glans surface exposed daily develops mild keratinisation and its threshold to external stimulation rises somewhat. This “habituation through exposure” is one example showing that sensitivity is not fixed but varies with environment, and many folk beliefs about glans sensitivity lack accuracy in failing to account for this variability.

Derivative forms and the slang system

In Japanese trade usage there are several subclassifications based on the morphological features of the glans. Kari-daka (“high goose”) denotes a form with a markedly raised coronal sulcus, often preferred in large-penis works; conversely kari-hiku (“low goose”) denotes a form with a modest ridge. Trade classifications also exist for the colour and shape of the glans surface: “pink glans” (pale in colour), “black glans” (markedly pigmented), “heart-shaped glans,” and “mushroom-type” (markedly raised coronal sulcus), used in genre classification of adult video and in art-style classification of doujin works. As a rare anatomical phenomenon there are pearly penile papules (papillomata penis), a physiological variant of granular small elevations around the coronal sulcus; they have no pathological significance, though early on they pose a problem of differentiation from condylomata.

Classification by mode of stimulation

Sexual stimulation of the glans can be sorted into several types by the subject and the mode of movement of contact: fellatio, centred on enclosure and suction by the oral mucosa; handjob, centred on grip and friction by the fingers; and paizuri, using compression and friction by the breasts. The quality of sensation changes with the combination of tissue and movement of the contact surface. Because the coronal sulcus and frenulum are concentration points of nerve endings, techniques that selectively stimulate these parts have been thematised repeatedly both in adult expression and in sex-technique guides.

Thematisation in sexual expression

In adult expression the glans functions as a central element of composition and staging. Oral contact in fellatio scenes, finger stimulation of the glans in handjob scenes, and glans-licking in parallel with cunnilingus: the frequency with which it is depicted as an object of stimulation is extremely high. On adult-video sets, the close-up of the glans is established as a core technique of “up” staging. The capture of the moment of ejaculation (the money shot), confirmation of the erect state, and the depiction of response to various stimulation: there are many scenes in which the state of the glans is the determining factor of screen composition. In erotic manga and doujinshi too, the differentiated drawing of the glans is an important element of art: the outline of the coronal sulcus, the texture of the skin, the engorgement at erection, and the movement at the instant of ejaculation are pursued for a matter-of-fact vividness.

Cultural references

Expression thematising sexual attention to and caress of the glans is widely confirmed in Japanese shunga. The works of Katsushika Hokusai and Kitagawa Utamaro repeatedly present compositions combining exaggerated depictions of the glans with the expression of a woman caressing it. This is not realistic depiction but a symbolised representation, yet it can be read as a historical source showing that the glans has long been recognised as a subject of both vision and touch.

Western classical sculpture, by contrast, tends to depict the penis as a whole deliberately small, and specialised emphasis on the glans is rare. In ancient Greek sculptural aesthetics large genitals were rather a symbol of irrational vulgarity, and idealised bodies were given small genitals. This contrasts with the way Japanese shunga moved toward exaggerating the step of the glans and coronal sulcus, a difference discussed as one example of the stylistic divergence in male-body representation between East and West.

The practice of circumcision too produces regional differences in the cultural positioning of the glans. In Jewish and Islamic spheres neonatal foreskin removal is widely performed as religious rite, and the permanently exposed glans is standard; in North America non-religious circumcision spread for medical and hygienic reasons in the twentieth century, while in many regions of Europe and East Asia non-circumcision is general. That bodily sensation and aesthetic evaluation around the exposure or covering of the glans differ by cultural sphere has this geographic distribution of practice as its background, and such regional differences in body-image are sometimes reflected in the differentiated drawing of the glans in doujin works and adult expression.

See also

• Inkei (penis)
• Penis
• Phimosis
• Fellatio
• Large penis