Henry Gray (18251861). Anatomy of the Human Body. 1918.
Actions.The simultaneous contraction of the two muscles serves to fix the central tendinous point of the perineum.
The Bulbocavernosus (Ejaculator urinæ; Accelerator urinæ) is placed in the middle line of the perineum, in front of the anus. It consists of two symmetrical parts, united along the median line by a tendinous raphé. It arises from the central tendinous point of the perineum and from the median raphé in front. Its fibers diverge like the barbs of a quill-pen; the most posterior form a thin layer, which is lost on the inferior fascia of the urogenital diaphragm; the middle fibers encircle the bulb and adjacent parts, of the corpus cavernosum urethræ, and join with the fibers of the opposite side, on the upper part of the corpus cavernosum urethræ, in a strong aponeurosis; the anterior fibers, spread out over the side of the corpus cavernosum penis, to be inserted partly into that body, anterior to the Ischiocavernosus, occasionally extending to the pubis, and partly ending in a tendinous expansion which covers the dorsal vessels of the penis. The latter fibers are best seen by dividing the muscle longitudinally, and reflecting it from the surface of the corpus cavernosum urethræ.
Actions.This muscle serves to empty the canal of the urethra, after the bladder has expelled its contents; during the greater part of the act of micturition its fibers are relaxed, and it only comes into action at the end of the process. The middle fibers are supposed by Krause to assist in the erection of the corpus cavernosum urethræ, by compressing the erectile tissue of the bulb. The anterior fibers, according to Tyrrel, also contribute to the erection of the penis by compressing the deep dorsal vein of the penis as they are inserted into, and continuous with, the fascia of the penis.
The Ischiocavernosus (Erector penis) covers the crus penis. It is an elongated muscle, broader in the middle than at either end, and situated on the lateral boundary of the perineum. It arises by tendinous and fleshy fibers from the inner surface of the tuberosity of the ischium, behind the crus penis; and from the rami of the pubis and ischium on either side of the crus. From these points fleshy fibers succeed, and end in an aponeurosis which is inserted into the sides and under surface of the crus penis.
Action.The Ischiocavernosus compresses the crus penis, and retards the return of the blood through the veins, and thus serves to maintain the organ erect.
Between the muscles just examined a triangular space exists, bounded medially by the Bulbocavernosus, laterally by the Ischiocavernosus, and behind by the Transversus perinæi superficialis; the floor is formed by the inferior fascia of the urogenital diaphragm. Running from behind forward in the space are the posterior scrotal vessels and nerves, and the perineal branch of the posterior femoral cutaneous nerve; the transverse perineal artery courses along its posterior boundary on the Transversus perinæi superficialis.
The Deep Fascia.The deep fascia of the urogenital region forms an investment for the Transversus perinæi profundus and the Sphincter urethræ membranaceæ, but within it lie also the deep vessels and nerves of this part, the whole forming a transverse septum which is known as the urogenital diaphragm. From its shape it is usually termed the triangular ligament, and is stretched almost horizontally across the pubic arch, so as to close in the front part of the outlet of the pelvis. It consists of two dense membranous laminæ (Fig. 407), which are united along their posterior borders, but are separated in front by intervening structures. The superficial of these two layers, the inferior fascia of the urogenital diaphragm, is triangular in shape, and about 4 cm. in depth. Its apex is directed forward, and is separated from the arcuate pubic ligament by an oval opening for the transmission of the deep dorsal vein of the penis. Its lateral margins are attached on either side to the inferior rami of the pubis and ischium, above the crus penis. Its base is directed toward the rectum, and connected to the central tendinous point of the perineum. It is continuous with the deep layer of the superficial fascia behind the Transversus perinæi superficialis, and with the inferior layer of the diaphragmatic