428 MYOLOGY 



Actions. The simultaneous contraction of the two muscles serves to fix the central tendinous 

 point of the perineum. 



The Bulbocavernosus (Ejaculator urince; Accelerator urines) 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 raphe. It arises from the cen- 

 tral tendinous point of the perineum and from the median raphe 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 urethrse, and join 

 with the fibers of the opposite side, on the upper part of the corpus cavernosum 

 urethrae, 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 cavernosuln urethrse. 



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 urethrae, 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 bound- 

 ary of the perineum. It arises by tendinous and fleshy fibers from the inner sur- 

 face 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 Bulbo- 

 cavernosus, laterally by the Ischiocavernosus, and behind by the Transversus perinsei super- 

 ficialis; 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 perinsei superficialis. 



The Deep Fascia. The deep fascia of the urogenital region forms an investment 

 for the Transversus perinsei profundus and the Sphincter urethrse membranaceae, 

 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 laminae (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 tri- 

 angular 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 perinaei superficialis, and with the inferior layer of the diaphragmatic 



