The _cavernous bodies_ form two tubes, united in most of the length of the penis, separated only by a thin partition, and enveloped in a firm sheath; they are composed of an immense number of cells, principally formed by dilated veins, which communicate with each other; these, when the penis is erected, become filled and even distended with blood. The cavernous bodies terminate abruptly and form rounded points under the glans penis. At the other extremity they separate, and form the crura or legs of the penis. The _spongy body_ forms the lower and under body of the penis, terminates at one end at the point in the glans, whilst it extends the whole length of the penis, again becomes enlarged, and forms the _bulb_. The urethra or water passage extends through the spongy body, and connects the penis with the bladder. This cut is a section of the penis showing the three bodies: [Illustration: _a._ Corpora Cavernosa. _b._ The division or Septum. _c._ Corpus Spongiosum. _d._ Urethra. _e._ The great vein of the Penis.] The cut below shows a section of the cavernous body, showing the blood vessels that go to it and cause a distension or erection of the penis: [Illustration: _a._ Urethric part. _b._ Glans. _c._ Dorsal Artery serving the Glans. _d._ Dorsal Artery serving the interior of the Corpus Cavernosum. _e, f._ Deep-seated Arteries.] [Illustration: _a._ Urethra. _b._ Glans. _c._ Dorsal Vein. _d._ Septum. _e._ Vessels.] In the cut above we see the septum or division of the cavernous bodies, in which are seen the vessels by which, when the erection of the penis subsides, the blood passes into the dorsal vein of the penis. The _Urethra_, or water passage, is the canal that passes through the spongy body to the bladder. The urine and semen pass through it. It is very elastic, and may be dilated so as to admit a large instrument to be passed into the bladder, and it contracts on the smallest. It is supported in its course by the spongy body and the prostate gland, between which is a portion unprotected, called the membranous portion. The passage varies in its size in different parts: thus it is rather contracted at the orifice, enlarges within, and for an inch again contracts, dilates nearer the bulb, diminishes at the membranous portion and near the prostate gland, and finally enlarges into the bladder. The cut opposite will show these parts.