The instrument of generation in men (commonly called the yard, in Latin, _penis_, from _pendo_, to hang, because it hangs outside the belly), is an organic part which consists of skin, tendons, veins, arteries, sinews and great ligaments; and is long and round, and on the upper side flattish, seated under the _os pubis_, and ordained by Nature partly for the evacuation of urine, and partly for conveying the seed into the womb; for which purpose it is full of small pores, through which the seed passes into it, through the _vesicula seminalis_,[4] and discharges the urine when they make water; besides the common parts, viz., the two nervous bodies, the septum, the urethra, the glans, four muscles and the vessels. The nervous bodies (so called) are surrounded with a thick white, penetrable membrane, but their inner substance is spongy, and consists chiefly of veins, arteries, and nervous fibres, interwoven like a net. And when the nerves are filled with animal vigour and the arteries with hot, eager blood, the penis becomes distended and erect; also the neck of the _vesicula urinalis_,[5] but when the influx of blood ceases, and when it is absorbed by the veins, the penis becomes limp and flabby. Below those nervous bodies is the urethra, and whenever they swell, it swells also. The penis has four muscles; two shorter ones springing from the _Cox endix_ and which serve for erection, and on that account they are called _erectores_; two larger, coming from _sphincters ani_, which serve to dilate the urethra so as to discharge the semen, and these are called dilatantes, or wideners. At the end of the penis is the _glans_, covered with a very thin membrane, by means of which, and of its nervous substance, it becomes most extremely sensitive, and is the principal seat of pleasure in copulation. The outer covering of the _glans_ is called the _preputium_ (foreskin), which the Jews cut off in circumcision, and it is fastened by the lower part of it to the _glans_. The penis is also provided with veins, arteries and nerves.