The testicles are created, as you know, as the two dominant organs in which the seed is generated from the moisture that seeps into them through the vessels and is, as it were, a surplus after the fourth digestion in the whole body, that is, the most mature and rarefied part of the blood. Pneuma sets this moisture in motion in the testicles and ducts leading to the testicles from beating and resting vessels. These vessels, in turn, branch from the large beating and large resting vessels, that is, from the main vessels, forming branches with many convolutions, bends and branches; if you cut one of these large vessels, it will be as if you have cut many vessels due to the abundance of stomata present there. Then the seed is poured out from the testicles through the seminal vessels, which we will talk about below, into the canal of the penis and from there it is thrown into the vagina of women - this is natural copulation. Then the seed rushes into the uterus, and the mouth of the uterus meets the seed, opening and drawing it in strongly if the eruption of male and female semen occurs at the same time. Testicles are hollow organs. The substance of the testicle is glandular tissue with white meat, most similar to the meat of the female breast: it is similar in color to the blood flowing to it and is therefore white, especially since the airy substance of pneuma is agitated in it. The channel through which the blood vessels approach the testicles is a large fold located on the pubis.
As for the membrane covering the arteries and veins that approach the testicles, it, as you learned in your place, grows from a large fold and as a result also connects with the membrane of the spinal cord. It descends through the vessels and suspensory ligaments, descending to the testicles through the inguinal canals; the channel is formed from this fold, passing through it, and from it a shell is formed that envelops the vessels that pass in the channels.
You already know from the anatomy of blood vessels that a different blood vessel approaches the left testicle than the one that brings nutrition to the right; the one that approaches the right testicle pours into it blood that is more mature and more purified from aqueous humor. The right testicle is stronger than the left in most people, with the exception of those who are left-handed. The seminal vessels begin like canals, along the canal from each testicle, and seem to be separated from it and are not formed from it, although they are adjacent to the testicle and are in contact with it. Near the testicle, each canal widens, forming a palpable cavity, then they begin to narrow again, although they widen again at the end, especially in women. These vessels first ascend and then join the bladder neck below the urinary canal.
As for the penis, it is an instrument organ formed from simple ligament organs, nerves, blood vessels and meat. Its growth begins with a body growing from the pubic bone, rich in ligaments and having numerous and wide cavities, which are mostly closed; when they are filled with winds, an erection occurs. Under this body there are many extensive arteries, larger than would be appropriate for the size of this organ. Nerves go to the penis from the vertebrae of the coccyx, which, however, do not lie very deep in the substance of the penis. The nerves of the substance of the penis are just ligaments, devoid of sensitivity; the nerves that cause the erection of the penis, according to Galen, are not those that relax it when it collapses. You have already learned about the special muscles of the penis from the paragraph on muscles. There are three canals in the penis: the urinary canal, the seminal canal and the erectile canal. Know that the force that causes an erection and the winds that carry it to the penis come from the heart, sensation from the brain and spinal cord, balanced blood and passion from the liver. The passion that is natural for him sometimes arises with the participation of the kidneys, but in my opinion, its basis is from the heart.