Anatomic Study of the Clitoris and the Bulbo-Clitoral Organ 2014th Ed.

5. Structure of the Bulbo-clitoral Organ

Vincent Di Marinoand Hubert Lepidi1

(1)

UER Médecine, Aix-Marseille Université, Marseille, France

Abstract

The description of structures referred to as “clitoral” represents a true semantic problem. When referring to the anatomical nomenclature, the old nomenclature or the recent international nomenclature, the clitoris and the vestibular bulbs are described separately.

5.1 Terminology Difficulties

The description of structures referred to as “clitoral” represents a true semantic problem. When referring to the anatomical nomenclature, the old nomenclature or the recent international nomenclature, the clitoris and the vestibular bulbs are described separately.

When considering anatomic facts, i.e. what is observed and what is revealed through dissection, the clitoris and vestibular bulbs are closely related and form a single entity, specific to the external female genital apparatus. However, difficulties arise in relation to the name of this entity.

O’Connell H.E. et al. solved the problem by referring to the two above-mentioned structures with a single term: the clitoris. However, if this is true from an anatomical observation viewpoint, it is inaccurate from a terminological viewpoint.1

The question becomes even more complicated when considering the glans, which is qualified (as is customary) by the adjective clitoral (due to the fact that, from a topographical viewpoint, it represents the free and exteriorised part of the clitoris), while, at the same time, it is embryologically derived, for its major part, from the primitive corpus spongiosum.

In order to solve all these difficulties, we propose to call this complex unit, derived from the female embryonic genital tubercle, the “bulbo-clitoral organ”.2 This unit was referred to by Testut et al. in their famous book on Anatomy, which has been published many times, as erectile organs of the vulva, which Köbelt had referred to by using a holistic term: genital senses apparatus in female.3

The bulbo-clitoral organ, such as it has always been observed, includes:

·               Cavernous structure parts: the crura and the body of the clitoris

·               Spongy structure parts or parts derived from the foetal corpus spongiosum: the vestibular bulbs, the commissure of the bulbs and the infra-corporeal residual spongy part

·               A part ensuring the junction and the communication between the cavernous and spongy vascular structures: Köbelt’s pars intermedia

This organ resembles a dihedron (Fig. 5.3) whose top edge comprises a slanted extension directed downwards and backwards. This dihedron caps a truncated urogenital pyramid consisting of the vaginal canal surmounted by the urethra. Overall, through dissections, the considerable significance of the buried parts of this bulbo-clitoral organ is rapidly observed. The vision of the glans clitoridis, alone free and visible part of the clitoris, only provides a minimalist overview of the said apparatus.

While the architecture of the bulbo-clitoral organ is constant, this is not the case for its global morphological aspect and a significant range of various aspects can be encountered, not only due to the various lengths, thicknesses and shapes of its components but also due to the variety of connection angles of these same components. At first sight, as soon as an anatomical sample has been collected and even after the most careful dissection of this specimen, the bulbo-clitoral organ has a massive aspect, which is always astonishing, and sometimes even a little monstrous (Fig. 5.1).

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Fig. 5.1

Morphology of the clitoral parts of bulbo-clitoral organs after resection of bulbs and spongy tissue. (a) Antero-superior view, usual aspect; (b) superior view, tapered aspect; (c) right lateral view, usual aspect; (d) right lateral view, usual aspect (the spongy part dissected, but always attached to the distal clitoris, is tilted forwards (curved white arrow)); (e) right lateral view: bulging aspect; (f) right infero-lateral view: usual aspect; (g) posterior view (with neurovascular hilum and very long crura)

Furthermore, this apparatus occupies the three dimensions (Fig. 5.1). This triplanar characteristic, which could only be demonstrated by 3D reproductions, requires, in relation to the pictures intended for the pages of a book, the use of artifices, such as contrast and light variations, or unusual shots such as right or left ¾ photographs (Fig. 5.2).

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Fig. 5.2

Lateral aspect of a dissection showing the structure of the bulbo-clitoral organ. bo body of the clitoris, descending part, bo′ body of the clitoris, ascending part, cr crus clitoridis, anangle (or elbow) of the clitoral body, h hood, p pubis, rsp residual spongy part, Vva vaginal vestibule. Arrowheads: They show the area of the intermediate network of Köbelt. Note: The red arrowhead indicates the part where this network’s communications are the most dense: between the commissura bulborum and the angle of clitoral body

5.2 Parts of Cavernous Structure

They are the crura and body of the clitoris.

5.2.1 The Crura

The crura clitoridis (international nomenclature), or pillars or roots, are the two cavernous structures, shaped as a long cornet, attached, via the ischiocavernosus muscles, to the ischio-pubic rami of the two coxal bones, which will meet frontwards and from within to form the body of the clitoris (Fig. 5.3). These crura are located at the anterior perineum in the superficial perineal region,4 in contact with the lateral edges of the subpubic angle. In order to reach them, it is necessary to cross the superficial fascia of the perineum, to almost completely free the labial fatty body,5 contained in the labia majora6and to push this formation towards the ventral surface of the pubis.

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Fig. 5.3

Dissection of the urogenital female perineum showing the bulbo-clitoral organ in situ. an angle (or elbow of the clitoral body), b bulb (spongiosus), bo body of clitoris, cr crus clitoridis, fcl frenum (frenulum clitoridis), g glans clitoridis, h hood, i-p r ischio-pubic ramus, lm labium minus (lesser lip), p pubis (anterior surface), pr prepuce, sl suspensory ligament, u external urethral orifice, va vaginal orifice (introïtus). The photography is taken in slightly ¾ right, in order to see the clitoral body

When the crura are still in place and not detached from their insertions, it is all the more difficult to apprehend their shape as they are hidden by the muscle fibres of the ischiocavernosus muscles, which are pushed against their lower and medial parts. Moreover, these crura are attached to the internal surfaces of the ischio-pubic rami. The lower edges of these rami partially hide the crura. Overall, it is actually only possible to study the crura when they have been released from their attachments and therefore only parts analysed ex situ (Fig. 5.4). There exists a right-left symmetry but when the two crura are examined on the sampled parts, a few discrete variations in length, thickness and sometimes, morphology, are observed. Each crus is initially tapered (top of the cone) and becomes gradually wider to reach its maximum diameter in front of the distal part of the ventral surface of the pubis, before joining the opposite crus on the centre line, in front of the pubic symphysis. The crura of the corpora cavernosa, with the ischiocavernosus muscles which cover them (which themselves are sheathed in their envelope fascia), make up structures solidly attached to the lateral edges of the pelvic outlet via bone and fibrous attachments. The bone insertions are located on the middle part of the internal surface of the ischio-pubic ramus, under the sickle-shaped crest7 and slightly above the lower edge of the bone. The fibrous insertions are located on the juxta-bone part of the lower fascia of the urogenital diaphragm (perineal membrane). At this level, the fascia clearly becomes thicker. We propose to call this thickening “attaching lamina of the corpora cavernosa”.

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Fig. 5.4

Dissection of a bulbo-clitoral organ showing the relationships between the different components (ventral view of an ex situ dissection). b bulb (spongiosus), cr crus clitoridis, f frenum (frenulum clitoridis), g glans clitoridis, lm basis of the labium minus, n dorsal nerve of clitoris, pr prepuce

The dimensions of the crura vary, we have already observed this! In our research, the average length of the crura (measured up to the level where the joining between the left and right crura starts) is of 37 mm (30 to 35 mm for L. Testut, 30 mm for P. Kamina). The average diameter (measured at mid-length of the crus) is of 9 mm for the parts which we have measured.

The structure of the crura is simple: a thick fibro-elastic or albuginea envelope, surrounding and protecting the cavernous tissue. It is the albuginea one, which provides the crus with its firm consistency. Each crus receives a feeding artery, a branch of the superficial perineal artery.

The two crura have a prepubic converging direction and their axes determine, between them, a connection angle, shaped as a reversed V, of variable amplitude, of 85° on average (extreme angles: 50 and 95 degrees)8 with, from an architectural viewpoint, a relatively ogival disposition. This connection is not a unitive convergence such as seems initially apparent. By examining the back of the sampled parts, the impression is given that there is a triangular commissure (Fig. 5.5), which merges together the terminal portion of the two crura. Actually, the dissection and sections (Fig. 5.6) are used to affirm that there is no fusion of the initial crura into a single corporeal element. There is no coalescence or fusion but only a joining of the two pillars, which will merge to form a single corporeal cylinder. As for the pseudo-commissure of the pillars, which it is better to call retro-crural fascia (old “ligament of the inter-thigh”), it is only formed by a single dense fibrous layer, which merges more or less with the fibrous coating, which coats the ventral surface of the pubic symphysis and from which it can be detached to unstick the clitoris from the symphysis and slightly rotate it backwards and downwards. This pseudo-commissure (Figs. 5.55.7 and 5.8) covers a trapezoidal or triangular surface (isosceles or equilateral triangle), of variable height (between 1.3 cm and 2 cm). The base of the commissural triangle borders the lower edge of the pubic symphysis. This fibrous structure is not only a unitive collagen lamina coating the dorsal surfaces of the crura. It is an actual protective tunic whose major role is to cover the nerves and vessels, before they reach the cavernous structures. This fascia delimits a loose conjunctive region, the retro-crural space (Fig. 5.9), inside which are routed small arteries, veinlets, nerve rami with, at their contact, many Pacini’s corpuscles. In this region, a median fibrous partition (aligned on the median septum of the clitoral body), separating the right and left vasculo-nervous contingents, is often observed.

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Fig. 5.5

Three-quarter view of an ex situ dissection of the bulbo-clitoral organ showing the reciprocal positions of clitoral and bulbar parts. b right bulb, b′ left bulb, bco bulbar commissure, boclitoral body, post-angular part (descending part), bo′ clitoral body, pre-angular part (ascending part), bco bulbar commissure, cr crus clitoridis, sl suspensory ligament, * the asterisk locates the retro-crural fascia

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Fig. 5.6

Photomicrographs of two transversalis sections of the corpora cavernosa into the clitoral body. (a) This section concerns the elbow (or angle) of the clitoral body. The CC of each crus is continuous with the CC of the corresponding half clitoral body. Note the round aspect and the great diameter of the cavernous gaps into the crura and the tight longitudinal meshes of clitoral body. The median septum thins towards the end of the post-angular body. (b) This section concerns only the post-angular portion of the clitoral body. The cavernous gaps only have tight longitudinal meshes. The 2 CCs separated by a median septum are incorporated in a single clitoral cylinder. a albuginea, bo clitoral body (post-angular part), cr crus clitoridis, ms median septum, sl suspensory ligament, black arrows they locate the cavernosal arteries (deep clitoral arteries)

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Fig. 5.7

Dorsal aspects of 2 bulbo-clitoral organs (ab), showing the retro-crural fascias with their triangular surface. an angle, b bulb, bco bulbar commissure, bo clitoral body, descending part (clitoral shaft), bo′ clitoral body, ascending part, cr crus clitoridis, h hood, r-cr f retro crural fascia, sl suspensory ligament, On the pictures (a′, b′), the triangular surface of each retro-crural fascia has been delimited by red lines

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Fig. 5.8

Relationships between the crura clitoridis, the bulbs and the urethra (dorsal view of an ex situ dissection of a bulbo-clitoral organ removed with the underlying urethra). an angle, bbulb, bo clitoral body, post-angular part (descending part), bo′ clitoral body, pre-angular part, (ascending part), cr crura clitoridis, g glans, r-cr f retrocrural fascia. The bulbar commissure draws an arch which creeps between the joined crura and the distal urethra’s dorsum

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Fig. 5.9

The retro-crural fascia and the retro-crural space. (a) Photomicrograph of a section of the joined crura of the clitoris showing the retro-crural space; (b) microscopic aspect (standard staining by HEAS); (c) microscopic aspect (PSA staining). a albuginea, CC corpus cavernosum, ms median septum, N bundle of the dorsal nerve of clitoris, r-cr f (with curved red arrow): retro-crural fascia, s′ septum of the retro-crural space, long thin red arrow it shows the retro-crural space, short thick red arrow it shows the microscopic aspect of the retro-crural fascia

5.2.2 The Body

Such as we have just observed, it is the joining of the two crura which will form the body of the clitoris. At the start, this body continues the direction of the crura, in front of the pubic symphysis. It then has a large diameter, representing the sum of the diameters of each clitoral crus. The joining of the medial surfaces of the two albugineae (Fig. 5.10) creates a true fibrous partition: the septum of the crura (pectiniform partition of Testut), which will extend into the corporeal clitoral cylinder, by the median septum. When it reaches mid-height of the ventral symphysis surface, the body of the clitoris will suddenly change directions and leave the bone plane and protrude downwards and backwards into a sagittal plane. This change of direction and plane corresponds to the angle or elbow of the clitoris. This elbow therefore belongs to the clitoris body, which it separates into two segments: a short segment, against the pubis, and a long segment, arranged on a sagittal plane, perpendicular to the symphysis plane. The entire body of the clitoris thus has, via lateral vision, a bent aspect, with a high convexity (Fig. 5.5), which sometimes recalls a sort of bump.

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Fig. 5.10

Photomicrographs of two sections of the crura clitoridis. (a) Transversal section just before backing (the medial parts of the tunicae albugineae are still separated and form the cavernous commissure). (b) Coronal section of the joined crura in the pre-angular part of the clitoral body (ascending part), showing the formation of the clitoral body (the medial part of the 2 tunicae albugineae has merged in a single median septum). a albuginea (tunica albuginea), CC corpora cavernosa, cr crus clitoridis, ms median septum, sl suspensory ligament, * retro-crural fascia

The angle or elbow (that L. Köbelt referred to as the knee) deserves to be studied with care, in addition to the fact that it corresponds to a significant change in direction, it has two major characteristics: It is the area to which is attached a major portion of the suspensory ligament (see relevant chapter). It is also the area from which the corporeal structure acquires its final volume and its cylindrical shape. This elbow corresponds to an angle, the Köbelt angle of inflection, 90° on average (extreme angles are of 85 and 150°). In most cases, the top of the angle is rounded. Sometimes, even the top of the angle is replaced by an arch or a small dented protrusion. This clitoral elbow is attached very solidly to the pubis, not only by the suspensory ligament of the clitoris but also via the retro-crural fascia backed to the prepubic fibrous coating.

The ascending segment (ascending part or pars ascendens) of the body of the clitoris, located upstream of the elbow, is the pubic segment (or pre-angular segment) of the body. It results from the joining of the 2 corpora cavernosas of the crura clitoridis. This segment is relatively short and does not exceed 2 cm (average length: 1.28 cm). Initially positioned against the pubic symphysis, it then slightly detaches therefrom while maintaining its slanted ventro-cranial orientation (Fig. 5.5). In this segment, the 2 corpora cavernosas of the crura still retain their cylindrical shape. They are tangents via the medial edges of their albuginea. However, the medial parts of the 2 albugineae will imperceptibly merge, as if forceps were applying lateral tensions and crushing the 2 cavernous cylinders against one other (Fig. 5.10). The 2 cylinders will take the shape of 2 tangent hemi-cylinders via their medial parts, which have become straight. Firstly, a true fibrous commissure is created, the cavernous commissure. Then, the albuginea will merge and cause the coalescence of the medial fibrous parts, which have become rectilinear. Thus are formed the double corpora cavernosa of the clitoral bodyand its septum, the median septum. It should also be noted that the relatively large cavernous cavities at the crura will tend to be packed inside the corpus cavernosum of the clitoral body and thus become narrower (Fig. 5.6) and occupy a smaller surface whereas their number has more or less doubled as it includes the cavities of the two crura! This cavernous structure is quite visible in the preputial segment or post-angular segment of the clitoral body (Fig. 5.11). This segment, with a descending direction (descending part of the clitoral body), is directed downwards and to the rear. The ¾ distal sections of this part of the clitoral body can be felt under the skin of the prepuce, at the interlabial groove. It is this part which is extended, as we have already observed, by a free end: the glans. This part of the body of the clitoris is sometimes referred to as the clitoral shaft. Anatomists, as well as gynaecologists, have not conducted many studies on the length of the clitoral body. During our work, we observed an average length of 1.28 cm for the pubic part and 3.24 cm for the shaft (the glans being excluded). If the glans is associated to the shaft, we obtain 3.75 on average for the entire descending part! Even less knowledge is available concerning the diameter of the clitoral body. It is true that the definition of this diameter is difficult and represents an immediate problem: Is the clitoral body to be measured with all its envelopes? Is it necessary to include the skin of the prepuce in the analysis of the diameter of the descending portion? Is it necessary to include the latero-corporeal fibres of the suspensory ligament when making measurements? Finally, we chose the least debatable type of measurement: that of the diameter of the clitoral body, completely stripped of its envelopes and therefore simply covered by its albuginea. The average diameter is then of 1.10 cm for the posterior third, which confirms the size reduction occurring after the elbow. Otherwise, as each root has an average diameter of 0.9 cm, we should have found for the body: 0.9 × 2, i.e. 1.8 cm. This diameter decreases further because the transverse diameter of each of the corpora cavernosa progressively decreases and the average diameter of the distal third of the shaft’s pars cavernosa is only of 8 mm (see comparative sections). Then, a very slight widening of the distal part of the body occurs; this corresponds to the transition towards the anatomical glans. Due to the fact that the insertion of the hood only rarely occurs at the junction of the corporeal cylinder and of the base of the anatomical glans, in most cases, the visible part of the glans (or free part) only corresponds to the end of this anatomical glans (see Fig. 5.12). The structure of the shaft results from its formation mode: merging of 2 crura and thus of 2 corpora cavernosas, which is perfectly visible on the sections perpendicular to the axis of the descending part of the body—2 corpora cavernosas, surrounded by a single peripheral albuginea, resulting from the merging of the 2 albugineae of the crura, are observed. These 2 corpora cavernosas, shaped as quarter moons, with rounded angles, are separated by the median septum(“pectiniform partition” of the previous authors) became the cavernous septum, resulting from the fusion or coalescence of the joining area of the albuginea from the two crura. This septum, such as the albuginea, is essentially formed by a dense collagen fibre network. It is an incomplete septum, allowing, without any difficulty, the communication of the blood flow between the 2 corpora cavernosas (Fig. 5.13). The 2 cavernous arteries are connected to this septum and arranged symmetrically thereto. We will study in detail, further in this document, the tissue of the corpora cavernosa in order to gain a better understanding of its operating mode whose finality is a clitoral erection. We can firstly say that many rami are located within the cavernous tissue but that larger nerve branches, as well as a great number of vessels, are routed on the lateral walls of the albuginea, in the direction of the glans. The cavernous cylinder and the vessels and nerves, which are routed along the cylinder, are surrounded by a thin conjunctive envelope: the clitoral fascia (Fig. 4.​7), analogous to the deep fascia described by Buck for the male penis. The neurovascular formations are not the only components, which can be found in abundance, around the corpora cavernosa. The body of the clitoris has a high content of sensory corpuscles, especially mechanoreceptors of Vater-Pacini (see Chap. 9). These corpuscles are located in a site in contact with the neurovascular bundles, which is not surprising as each mechanoreceptor contains a sensitive nerve fibre.

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Fig. 5.11

Transverse section of a bulbo-clitoral organ showing the structure of both the clitoral body and the glans (the superior half of the body is slightly tilted upwards by a forceps, in order to see the inferior section’s surface). bo clitoral body (descending part), CC joined corpora cavernosa, cr crus clitoridis, g glans clitoridis, h hood, ms midline septum, black arrowheadneck of the glans. Note the gradual reduction of the joined corpora cavernosa’s diameter which become very sharp at their distal end

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Fig. 5.12

The end of clitoral body and the glans. (a) Photomicrograph of a transverse section of the end of the body’s descending part. (b) Microscopic aspect of g′ (hidden part of the glans or end of the body for other authors). (c) Photomicrograph of another specimen (section similar to a). a tunica albuginea, bo clitoral body, descending part, CC corpora cavernosa, FlForster’s ligament, g glans (free end), g′ glans (hidden part), h hood, ms median septum. The dotted and bound white lines delimit what is considered by many authors as the hidden part of the glans. Note also the peniform morphology of the glans c

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Fig. 5.13

Photomicrograph of a bulbo-clitoral organ’s frontal section at the angle of clitoral body. b bulb (corpus spongiosum), bco bulbar commissure, bo clitoral body, CC conjoined corpora cavernosa, CScorpus spongiosum, ms median septum, separating the two conjoined corpora cavernosas, pi pars intermedia of Köbelt, pr prepuce. NB: on this section, it is evident that the two constituent parts of the female organ (corpora cavernosa and corpora spongiosa) form an unified structure: the bulbo-clitoral organ

·               The “top” part of the corporeal cylinder has key connections: The dense and most ventral fibres of the suspensory ligament of the clitoris are attached to its proximal part, beyond the elbow, such as they are attached to the latter. This is also the case of, when they exist, the fibres of the fundiform ligament of the clitoris, of which many pass on lateral surfaces of the body (see Chap. 9). Its distal half is superficial and subcutaneous: It is the back of the clitoral shaft, which can be felt beneath the ventral commissure of the lips, covered by the skin of the prepuce. Between the preputial subcutaneous tissue and the clitoral fascia, some neurovascular structures are observed: the superficial vessels and nerves of the clitoris (Fig. 12.​3). A microscopic study also shows, at this level, some smooth muscle fibres similar to those of the dartos of the penis, as well as large tact corpuscles.

·               The “bottom” part of the corporeal cylinder is in direct connection with the commissure of the bulbs as well as with the infra-corporeal residual spongy part. These spongious structures are connected to the body of the clitoris via the network or pars intermedia described by Köbelt.

5.3 Parts of Spongy Structure

These structures are the “vestibular” bulbs joined together by the commissure of the bulbs and the infra-corporeal residual spongy part.

5.3.1 “Vestibular” Bulbs

It is undeniable that the two bulbs belong to the bulbo-clitoral organ, as opposed to what can be read in certain books on anatomy, even the best known works,9 while at the same time Köbelt thought that he had definitely demonstrated this connection since 1851. After the work published by Köbelt, other vicissitudes awaited the bulbs, whose name changed from one author to another over time, from the “plexus retiform” terminology to that of “vestibular bulbs”, which has been employed by the commissions of the anatomical nomenclature, including terms such as “vaginal bulbs” (Testut) or “urethral bulbs” or even “urethro-vaginal bulbs”, which is better suited to anatomical facts (see Chap. 13).

The 2 bulbs are generally represented as two bulky, long, curved and convex formations, which are convex on their bottom surface, via which they are discovered during a perineal dissection (Fig. 5.3), once the superficial perineal fascia (fascia of Colles) has been broken down and the labial fatty body, which hides them, has been dissected and folded forwards. This is why, the bulbs have been graphically compared to “2 leeches full of blood” (Köbelt), positioned against the urethro-vaginal pyramid (see Fig. 5.3), laterally bordering the external orifice of the urethra and the vaginal orifice (introïtus), arranged diagonally and directed frontwards and inwards. The curved aspect may sometimes concern the bottom surface as well as the top surface: In such a case, the bulb takes the aspect of drop-shaped pendant, determining a sort of small latero-vaginal cavity. The bulbs may also have a more or less flattened shape, which is hardly convex on its bottom surface and is comparable to a flattened dry fig (Fig. 5.4), with a tapered antero-medial end and a large swollen posterolateral end. The dimensions of the bulbs are extremely variable: 3.15 cm on average with extreme measurements of 1.5 and 4.2 cm. The greatest width, generally located near the posterolateral end, is on average of 2.2 cm on average with extreme widths of 1.3 and 3.2 cm. The thickness varies on average between 3 mm (flattened bulbs) and 11 mm (bulging bulbs). The 2 bulbs are rarely perfectly symmetrical. Similarly, in most cases, the dimensions measured on the right and on the left vary considerably. The top surfaces of the 2 bulbs are in a supero-medial plane and include two insertion areas, which are sometimes separated by a small edge: an insertion on the lateral edges of the distal ends of the urethra and vagina and an insertion on the bottom fascia (perineal membrane) of the neighbouring urogenital diaphragm. The lower surfaces of the bulbs are in a slightly oblique, infero-lateral plane and are hidden by the fibres of the bulbospongiosus muscles applied to their albuginea. For each bulb, a lower medial edge (urethro-vaginal edge or vestibular edge) and an upper lateral edge directly connected to the crura of the clitoris are described. These edges are blunt and rounded. The posterolateral ends of the bulbs (which are sometimes referred to as the “bases” of the bulbs) are in contact with each great vestibular Bartholin’s gland, which they cap in a frontal region (Fig. 13.​2). When the bulbs are relatively symmetrical and short, the tangent at their base passes via the centre of the introïtus. The antero-medial ends (which are sometimes referred to as the “top” of the bulbs) are interconnected by the commissure of the bulbs (bulbar commissure). The bulbar commissure is, unlike the “pseudo-cavernous commissure”, a true commissure (Figs. 5.5 and 5.13) each bulb merges with the bulb on the opposite side via a true intermediate spongious bridge: the “fer à cheval à extrémité postérieure” (“horseshoe with a posterior end”) described by Grégoire.10 This flattened bridge, with a concave end section, penetrates between the junction angle of the 2 crura clitoridis and the anterior surface of the distal urethra.11 It thus forms a sort of Roman arch in the ogival region resulting from the convergence of the two clitoral crura (Fig. 5.5). The anterior end of the 2 bulbs and the bulbar commissure form, on the dorsal views, a nearly perfect half-circle (Fig. 5.8) whose diameter significantly varies (between 2 and 4 cm) according to the anatomical arrangement, the shape and the axis of the bulbs. The distal terminal part of the urethra passes under this spongy tunnel (Figs. 5.8 and 13.​1). Such as the bulbar commissure curvature differs from the straightness of the clitoral crura and from their angular convergence, other differences appear between the bulbs and the crura of the clitoris: The crura and their junction, in a more cranial location, seem to overlap the bulbs and their commissure. The large axis of the bulbs and that of the crura cross each other and form an extended X. While the crura, positioned against the ischio-pubic rami, have an axis, which is close to the lower edge (the axis of this bone segment), the bulbs, which are less oblique and sometimes almost vertical, are practically perpendicular to the large vaginal axis (Fig. 5.5).

It should be recalled that from a histological viewpoint, the bulbs and their commissure consist of a spongy tissue, wrapped in a thin connective tissue sheath, the bulbar albuginea, which does not have the thickness or the mechanical characteristics of the albuginea of the corpora cavernosa. The bulbs are residues of the deep part of the foetal corpus spongiosum which, due to the female genital dehiscence, has positioned itself “where it remains in place”, i.e. on either side of the urethral and vaginal ducts. Thus are explained the differences in size and shape existing between the right and left bulbs, the available volume not being automatically identical on either side.

The commissure of the bulbs is not, as could be believed according to the photos of dissected parts, dissociated from the clitoris beneath which it penetrates. As has been pointed out from the start, in this chapter, the spongy and cavernous formations belong to a single bulbo-clitoral organ. The anterior surface (“back”) of the commissure of the bulbs is closely connected to the posterior surface of the body of the clitoris at the inflection angle between the ascending and descending segments of the body. The junction area, well known since Köbelt, is called, such as has already been noted, the pars intermedia.

Moreover, the commissure of the bulbs has an extension, which protrudes downwards and backwards, under the post-angular descending part of the clitoral body, in the direction of the glans. This extension is also a residue of the foetal spongy tissue. We propose to call it the infra-corporeal residual spongy part.

5.3.2 Infra-corporeal Residual Spongy Part

This portion (icrsp or by abbreviation, rsp), which is not well known and often forgotten, remains an important component of the bulbo-clitoral body. Recognising this part is essential as its existence facilitates the understanding of the organogenesis of the apparatus itself. This extension of the bulbar commissure (Fig. 5.14), which has an irregular aspect and a diameter nearly equal to that of the cavernous cylinder of the clitoral body, follows the posterior edge of this body, to which it is closely connected via the distal part of Köbelt’s pars intermedia. It resembles a cord of spongious tissue, which is more or less involutive due to the anarchistic architecture including irregularly arranged gaps and a conjunctive interstitial tissue, which is more abundant than in the bulbar spongy tissue. This spongy portion, which is “infra-corporeal” on the parts studied ex situ, deserves to be qualified as “residual” because it is what remains from the foetal corpus spongiosum, whose initial purpose (surrounding the phallic urethra and the urethra of the glans) could not be fulfilled due to the involution of the above-mentioned urethral portions, but which has remained connected to the corpora cavernosa in their development in the clitoris, such as for men in relation to the formation of the penis. The similarity exists up to the glans, which will be formed by the spongy tissue. This is the case for men and women.

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Fig. 5.14

Advanced dissection of a bulbo-clitoral organ (view of ¾ right) with an almost complete separation of the spongy and cavernosa parts. The spongy part is lightly moved forwards (red curved arrow). CC corpus cavernosum, CS corpus spongiosum, an angle (or elbow), b bulb (spongiosus), bo body of the clitoris (descending part), bo′ body of the clitoris (ascending part), cr crus clitoridis, f frenum (frenulum clitoridis), g glans clitoridis, h hood, rsp residual spongy part, sl suspensory ligament, white arrowheads they show two vascular openings of the intermediate network of Kobelt

This extension was especially studied by A.A.W.M. van Turnhout et al. who were able to use many samples from plastic surgery operations related to “transgender” transformation (from woman to man). At the time of these operations, referred to as metoidioplasty (or metaoidioplasty) surgery, the clitoris, hypertrophied by a preliminary hormonal treatment, is transformed into a penis, and one of the surgical stages involves resecting the spongy tissue of the icrsp, which forms a sort of indurated cord under the body of the clitoris. For our part, we could, on each laboratory specimen, perfectly identify this infra-corporeal residual spongy extension of the bulbar commissure, ending at the glans of the clitoris. All of all the spongy structures also have a relatively surprising aspect (Figs. 5.2 and 5.14) recalling a sort of monstrosity and the anatomist can only be disconcerted by the contrast between this aspect and the delicate appearance of the free part of the glans, which luckily is the only part which is visible!

The icrsp communicates with the cavernous cylinder of the clitoral shaft, such as the commissure of the bulbs communicates with the corpora cavernosa at the corporeal inflection angle. However, for the icrsp, the connection vessels of the pars intermedia are shorter and more spaced out.

The vestibule, which is more posterior, is located immediately beneath the icrsp and the vessels of its lateral walls also communicate with the icrsp. The vessels of the spongy tissue diverge when they meet the ridge of the vestibular cavity (Fig. 5.15) and separate to penetrate the thickness of each wall of the vestibule and develop communications with the vestibular vessels which, in turn, are anastomosed with those of the labia minora. This explains the well-known contribution of the labia minora to the physiological modifications occurring during the sexual excitation phase in women. Overall, this represents continuity between the corpora cavernosa of the clitoral body, pars intermedia, bulbs and icrsp or between icrsp and vulvar vascular network (Fig. 5.15).

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Fig. 5.15

Position of the pars intermedia of Köbelt on a frontal section of a bulbo-clitoral organ. (a) Level of the section (ventral view of a bulbo-clitoral organ); (b) enlargement of the section’s surface. The section, perpendicular to the axis of the clitoral body, interests the clitoral shaft (descending part of body). b bulb, bo clitoral body (pars descendens), CC corpora cavernosa, cr crus clitoridis, CS corpus spongiosum (residue), pi pars intermedia (Köbelt), rsp residual spongy part, sl suspensory ligament, black and red arrowheads showing the end of the vestibule’s roof

5.3.3 The Pars Intermedia

It was perfectly described in 1851 by Köbelt in his book entitled De lappareil du sens génital des deux sexes (“About the genital sense apparatus of both sexes”. Despite the limited technical means of the time, the drawings of this “pars intermedia” (see Fig. 5.16) carried out by this author according to his dissections are astonishingly accurate and comply perfectly with the histological, anatomical and radiological documents, which we, happy researchers of the twenty-first century, have at our disposal! This network is particularly dense at the junction point between the commissure of the bulbs and the clitoral inflection (elbow of the clitoris). At the corner junction angle, the pars intermedia is dense and spread out and generally consists of 2 rows of more or less sinuous vertical veins, the majority of which are large, separated by a thick median fibrous septum and aligned on the cavernous septum, which it seems to extend (Figs. 5.17 and 5.18). The height of the venous rows and their median septum is variable, but in most cases, it is equivalent to that of the median septum of the clitoral body (cavernous septum). The veins of the pars intermedia connect the junction area of the crura clitoridis and 2 bulbs (Fig. 5.17). They are nearly always large and have a longitudinal axis (parallel to that of the septum). More rarely, these anastomotic veins form an actual venous maze (within which the septum is no longer visible), which provides a nearly direct communication between the spongy and cavernous tissues of the bulbo-clitoral organ. The pars intermedia is not limited to the inflection angle of the clitoral body. It extends up to the distal end of the body of the clitoris, thus developing a close connection between the corpus cavernosum of the clitoral body and the infra-clitoral residual spongy part. It is, however, less dense and more dispersed than at the inflection angle. At this level, it has an aspect, which has already been perfectly described by L. Köbelt: “double symmetrical row of venous communications, which are directed towards the lower surface of the body of the clitoris, where they penetrate”. The vascular orifices corresponding to the cross section of these vessels, when separated by dissection, the cavernous part of the body and the icrsp, are perfectly visible, even to the naked eye (Fig. 5.14). The lateral veins (also described by Köbelt), which “surround the lateral surface of the body of the clitoris” to reach “the dorsal vein of which they form the lateral roots”, also develop from this pars intermedia.

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Fig. 5.16

The communicating vessels of the pars intermedia (red arrow) (drawing of Köbelt’s book)

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Fig. 5.17

Frontal sections of 4 bulbo-clitoral organs. Photomicrographs showing the aspects of the pars intermedia (the connections with the bulbs are well visible only on a specimen). b bulb, bco bulbar commissure, CC corpora cavernosa, CS corpus spongiosum, pi pars intermedia, ° median septum of CC, * septum of the pars intermedia. On (ac), the septa of CC and of the pars intermedia are aligned. On (d), the aligning is less evident and the vessels more plexiform

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Fig. 5.18

The septa of the bulbo-clitoral organ’s erectile bodies (frontal section of a bulbo-clitoral organ). b bulb, CC corpora cavernosa clitoridis in the clitoral body, ms median septum, red arrowhead septum of the pars intermedia, red arrow septum into the bulbar commissure. Note: The aligning of the septa. An old haematoma visible into the left bulb

However, Köbelt’s network is not the only means of communication and fusion of the cavernosa and spongiosa corpora. There also exist interpenetrations between these 2 erectile components and areas, which the spongy venous lakes penetrate directly within the small cavernous cavities, without any intermediate vascular interposition, which can be clearly seen by microscopic observation (Fig. 5.17). This refers once again to the existence of a single bulbo-clitoral organ where the 2 erectile tissue components are not only connected but closely related.

5.3.4 The Glans

Although its free part has already been studied in the “morphology” chapter (Chap. 4), the glans, a very particular formation, deserves a global structural study. The glans, which derives, as we have observed, from the genital tubercle, such as the male penis, consists of, such as the latter, a spongy tissue. However, the lack of any “hollowing” of a pre-meatic urethra has contributed, such as for the infra-corporeal residual spongy part, which did not find a phallic urethra below the corpus cavernosum of the clitoral body, to modifying this spongy tissue of the genital tubercle. This tissue has persisted but has an in fine, involutive aspect, such as the “icrsp”, which it extends. This explains the numerous discussions on the erectile or non-erectile character of the glans, reported by R. Stefani et al.

In any event, from a structural viewpoint, two parts of the glans can be identified (Fig. 5.12):

·               The distal part or free part, consisting only of a specific but involutive spongy tissue, covered with a non-keratinised squamous epithelium, and to which is attached the preputial hood and glans frenula.

·               The proximal part, which is not visible and is a sort of hidden part of the glans, inside which terminate the tapered distal ends of the corpora cavernosa of the clitoral body, which are always separated by the median fibrous septum. However, the complexity of this proximal part of the glans does not end here.

·                      Firstly, the cavernous septum (median septum) extends beyond the cavernous ends, thus forming the ligament described by Forster,12 which opens up in the distal glans into several bundles (such as sort of palm tree) (Fig. 5.12), thus forming a true fibrous reinforcement of the clitoral glans (this reinforcement is even capable of reaching the end of the free glans).

·                      Otherwise, this arrangement only occupies the “upper” half of the glans, at the level of the plane of the corpora cavernosa. The “lower” half (Figs. 5.19 and 5.20) is only occupied, such as the free part of the glans, by the involutive spongy tissue.

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Fig. 5.19

Lateral view showing the two constituents of a bulbo-clitoral organ. Red legends for spongy tissue (Two transverse Sections A and B have been made in the axis of RSP, in order to observe its architecture (see photomicrographs of these transverse sections)). Blue legends for cavernous tissue. an angle, b bulb, bo′ clitoral body, pre-angular part (ascending part), boclitoral body, post angular part (descending part), cr crus clitoridis, rsp residual spongy part, sl suspensory ligament

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Fig. 5.20

Photomicrograph of the transverse section A through the RSP of the clitoral body’s post-angularis part (see the level of section on the previous picture). Photomicrograph of the transverse section B through the RSP of the clitoral body’s post-angularis part. Microscopic aspects of the spongy tissue of the RSP on frontal Sections 1, 2 and 3

Overall, the clitoral glans benefits from tumescence possibilities, which allow both its vascular structure and its location (as it caps the end of an erectile clitoral body, to which it is attached by a fibrous reinforcement!).

Footnotes

1

1The Unicist Theory, rehabilitated by O’Connell, corresponds to reality (see the histological dissections and sections…). However, the fact of referring to the two structures as the clitoris does not correspond to “nomina anatomica” and does not make sense; it is therefore a source of confusion.

2

2We chose the “bulbo-clitoral” adjective (“bulbo-clitoridien” in French) rather than the “clitorido-bulbar” adjective (“clitorido-bulbaire” in French), as it is easier to pronounce and translate into English.

3

3L. Köbelt had grouped the cavernous and spongy units under the same term “Genital Sense’s Apparatus in Female”, a consensual term which is too far removed from descriptive anatomy.

4

4The superficial perineal region lies between the superficial fascia of the perineum (fascia of Colles) and the lower fascia of the urogenital diaphragm (perineal membrane).

5

5The labial fatty body, a considerably vascularised fatty formation, which can be perfectly mobilised and can maintain an excellent vascularisation, if its upper pedicle is preserved, is used successfully, in surgery, for curing vesico-vaginal fistula (operation of Martius).

6

6The labia majora, due to their contents, were called “fatty bags” by the anatomist Marie Philibert Constant Sappey (1810–1896).

7

7The sickle-shaped extension of the sacro-tuberal ligament inserts itself into this sickle-shaped crest.

8

8In one case, among the 30 that we studied, the 2 crura had a hardly ascending and nearly horizontal route, and a connection angle exceeding 150°. This case was excluded from the previous average.

9

9Thus, in the impressive treaty of Bourgery and Jacob, the bulb is not described in the “clitoris” paragraph but in the “structure of the vagina” paragraph (see the chapter on “female genital apparatus”. Organes génitaux de la femme, in Tome V, Slanchnologie, p. 277–304 et planches 63à 75).

10

10The median septum of the pars intermedia may extend at the bulbar commissure and thus outline the formation of the bulbar septum. However, the latter is never complete and significant left-right direct communications persist between the 2 bulbs.

11

11See Chap. 13, the very close connections between the bulbar commissure and the urethral wall and Bibliography: M.S. Baggish et al.

12

12This ligament is often reinforced by a fibrous contingent from one or the two halves of the albuginea.