Now that we've seen the perineal muscles, we'll take a further look at the base of the penis. To see the bulb and crura more clearly we'll remove the bulbo-spongiosus, and ischio-cavernosus muscles.
The crura of the penis are the proximal extensions of the corpora cavernosa. On this side we've kept intact the dense outer covering of the crus, the tunica albuginea, which is firmly attached to the ischio-pubic ramus. On the other side we've removed the tunica, to see the erectile tissue of the crus.
The bulb of the penis ends in a convexity that faces backwards. The urethra enters the bulb from above. To see it, we'll remove the bulb of the penis. This gives us a clear view of the perineal membrane, which stretches between the ischio-pubic rami.
Here's the membranous urethra coming through the perineal membrane, surrounded by the external sphincter muscle. Blood vessels and nerves that supply the base of the penis pass through the perineal membrane.
Now we'll move on to take a look at the male urethra. In the previous section of this tape, we've seen the isolated bladder, and the prostate, with the urethra beginning here, at the internal urethral meatus and running down through the prostate.
We've also seen the bladder, and prostate from the side, with the urethra emerging below the prostate, passing though the pelvic diaphragm and perineal membrane and into the bulb of the penis. To see more of the urethra we'll look at an isolated specimen of the bladder, prostate and penis, that we'll divide in the midline.
Here's the urethra. It's described as having four parts, the prostatic urethra that runs through the prostate, the short membranous urethra that passes through the perineal membrane, the curving bulbar urethra in the bulb of the penis, and the penile urethra.
The membranous urethra is surrounded by a sleeve of striated muscle, the external urethral sphincter, which exerts voluntary control on the passage of urine. The penile urethra passes along the corpus spongiosum and through the glans, ending at the external urethral meatus.