When the labia and nymphm are abscised a series of vascular erectile structures are brought into view, which, together with a special muscle, surround the vaginal orifice. These are the vestibular bulb, pars intermedia, and constrictor vagin(e muscle, Pars intermedia.—From the dorsal vein of the clitoris (fig. 481. d) several branches (n,n) pass downwards round the sides of the organ • to communicate with a double row of closely set venous canals, which commencing ante riorly at the glans extend backwards to the root of the clitoris in the form of a frill that completely occupies the angle contained in the curvature of the organ (fig. 481. M and fig. 482.f). These venous canals enter the body of the clitoris by a double row of' apertures along its under surface. They represent the communicating veins between the corpus spongiosum urethrte and the corpora caver nosa penis. After receiving branches from the glans clitoridis (fig. 481. /), nymphm (r), and labia (p), they form on either side a series of convoluted veins (k), which spread ing downwards and outwards ultimately termi nate below in the bulb of the vestibule (fig. 482. and 483. a). This is the structure termed by Kobelt the pars intermedia. It corresponds with the corpus spongiosum ure thrm of the male, which in the female remains divided into two halves. The arteries of this structure (fig. 481. q) are derived from the pudendal.
Bulbus vestibuli (Kobelt). Plexus retiformis v. reticularis (De Graaf). Crura clitoridis in terna (Swammerdam). Plexus cavernosus (Tabarranus). Corpus cavernosum (Santorini). Sernibulb (Taylor). Bulb of the vagina. — Lying one on either side of the entrance to the vagina, and behind the nymphte and labia, are two masses of vascular parenchyma, composed almost entirely of tortuous veins enclosed in a fibrous membrane. These in their collapsed state are of the size and form of an almond; but when injected may be compared to a filled leech (fig. 482. and 483. a). Anteriorly they are directly continuous with the structures last described, while from their sides commu nicating branches pass back to the obturator veins (fig. 483. /), and from their lower ends to the pudendal and htemorrhoidal veins (fig. 482. b and c). The bulb of the vagina, now commonly regarded as the homotype of the bulb of the urethra which is here bipartite, forms the principal portion of the erectile tis sue surrounding the vaginal orifice.
Constrictor vagina.— The clitoris together with its bipartite pars intermedia and vestibu lar bulb is encased in a thin sheet of mus cular structure (fig. 483. b and c), which has been usually regarded as the constrictor of the vaginal orifice, but which Kobelt considers to be more particularly employed as a com pressor of the parts just named. This muscle takes its origin in a broad flattened base (b) from the perineal fascia midway between the anus and tuber ischii. The inner fibres inter lace with those of the sphincter ani, while the outer ones reach to the corresponding ascend ing ischial ramus. Thence the muscle be comes gradually smaller as it ascends, and after embracing the entire length and breadth of the vestibular bulb, it converges forwards to meet its fellow at the clitoris, where it termi nates in two little flattened portions of which the posterior passes as a narrow tendon (fig. 483. d) to unite with its fellow between the upper end of the bulb and the root of the clitoris, while the anterior looser portion (c) mounts over the dorsum of the clitoris, form ing the musculus attrahens clitoridis. This
serves to depress the organ and compress the dorsal vein, at the same time that the lower portion of the same muscle, by com pressing the rest of the vascular apparatus, forces the blood out of the vestibular bulb and pars intermedia upwards into the body of the clitoris, and thus aids in producing congestion and erection of all these parts during coition.
Blood-vessels of Me external organs.— The arteries are supplied by the terminal branches of the internal pudics and from branches of the femoral.
The pudic sends off two branches : the first, or lower (superficial perineal branch ), terminates in the labium after suppbing the sphincter vaginw and some of the perineal muscles. The second, or superior, mounting along the ischio-pubic rami to the division of the crura clitoridis, sends off a branch (artery of the bulb) to the bulbus vestibuli, and then separates into two terminal twigs, the one (profitnda branch) entering the cavernous sub stance of the clitoris, while the other forms the dorsal artery of that body (fig. 481. h).
The femoral supplies the external pudica, two in number on each side, which arise by a comnion trunk or singly from the inner side of that vessel. The superior of these branches (superior pudenda externa)arises near the cru ral arch and, passing inwards, sends off two branches, one to the mons veneris and lower part of the abdominal integuments, the other, terminating in the labium, sends also twigs to the nympha and preputium clitoridis. The inferior branch (inferior pudenda externa), arising a little below the former, or from the profunda, passes obliquely tom ards the labium in which it terminates, anastoinosing also with the superficial perineal branch of the pudic.
Veins.—The veins of the clitoris and the venous plexuses surrounding the vaginal orifice, together with their communicating branches, have been already described. The external pudic veins, collecting the blood from the mons veneris and the interior of the labia, take a course similar to that of the correspond ing arteries, and empty theniselves into the saphena.
The lynzphatics of the external organs ter minate in the inguinal glands.
The nerves.—The external parts are abun dantly supplied with nerves derived chiefly from the pudic. Tbe pudic nerve arising from the lower part of the sacral plexus passes through the sacro-sciatic foramen and accom panying the pudic vessels divides into two branches.
The inferior, or perineal branch, sends twigs to.the labia, nymphai, and roots of the clitoris, and then gives off the superficial perineal branch, which is distributed to the constrictor muscle of the bulb of the vagina.
The superior, or branch of the clitoris, corre sponds with the dorsal nerve of the penis. Beneath the pubic arch it passes between the roots of the clitoris and is distributed along the side of that organ in the manner already described Vg. 481. ii). Some of its ramifica tions are distributed upon the prepuce and in the nymphm and upper parts of the labia.
The labium also receives nerves from the branches of the inferior pudendal nerve, a di vision of the small sciatic nerve. These com municate with the superficial perineal branches.