OF THE PERINEUM IN THE E EM ALE 445 



point its fibres diverge symmetrically ; the most posterior form a thin layer, which 

 is lost on the superficial surface of the triangular ligament; the middle fibres encircle 

 the bulb and adjacent parts of the corpus spongiosum, and join with the fibres 

 of the opposite side, on the upper part of the corpus spongiosum. in a strong 

 aponeurosis. The anterior fibres, the longest and most distinct, spread out 

 over the sides of the corpus cavernosum, and are inserted partly info that body. 

 anterior to the Erector penis (occasionally extending to the os pubis), and partly 

 terminate in a tenr|inons pvpnpsinn. which covers the dorsal vessels of the penis. 

 The latter fibres are best seen by dividing the muscle longitudinally, and dissect- 

 ing it outward from the surface of the urethra. Many fibres of the External 

 sphincter ani and of the Superficial transverse perineal muscles pass into this 

 muscle. 



Action. 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 fibres are relaxed, and it only 

 comes into action at the end of the process. The middle fibres are supposed, by Krause, to 

 assist in the erection of the corpus spongiosum, by compressing the erectile tissue of the bulb. 

 The anterior fibres, on each side, according to Tyrrel, also contribute to the erection of the 

 penis, as they are inserted into, and are continuous with, the fascia of the penis, and thus com- 

 press the dorsal vein during the contraction of the muscle. 



The Erector penis (m. ischiocavernosus] covers part of the crus penis. It is an 

 elongated muscle, broader in the middle than at either extremity, and situated on 

 either side of the lateral boundary of the perineum. It arises by tendinous and 

 fleshy fibres from the inner surface of the tuberosity of the ischium^ behind the 

 crus penis, from the surface of the crus, and from the adjacent portion of the 

 ramus of the ischium. From these points fleshy fibres succeed, which end in 

 an aponeurosis which is inserted into ^he sides and under surface of the cms 

 penis. 



Nerve-supply. The perineal branch of the internal pudic. 



Actions. This muscle 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 internally by the 

 Accelerator urinae, externally by the Erector penis, and behind by the Transversus perinei 

 superficialis. The floor of this space is formed by the triangular ligament of the perineum (deep 

 perineal fascia), and running in it from behind forward (toward the pubis) are the superficial 

 perineal vessels and nerves, the lonpr pudenda! "erve r and the transverse perineal artery, which 

 courses along the posterior boundary of the space on the Superficial transverse perineal muscle. 



The Muscles of the Perineum in the Female. 



Superficial transverse perineal. Erector clitoridis. 



Sphincter vaginae. Compressor urethrae. 



The Superficial transverse perineal (m. transversus perinei superficialis} in 

 the female is a narrow slip which passes more or less transversely across the back 

 part of the perineal space. It arises by a small tendon from the inner and fore part 

 of the tuberosity of the ischium, and, passing inward, is inserted into the central 

 point of the perineum, joining in this situation with the muscle of the opposite 

 side, the External sphincter ani behind, and the Sphincter vaginae in front. 



Nerve-supply. The perineal branch of the internal pudic. 



Actions. By their contraction these muscles serve to fix the central tendinous point of the 

 perineum. 



