2. The membranous portion (h) extends from the prostate portion to a point between the crura of the penis. This portion is surrounded by the thick compressor urethræ muscle, so that its wall appears much thicker than it really is.
3. The spongy portion (pars cavernosa) extends along the ventral side of the penis to its end in the groove between the corpora cavernosa penis. At its beginning is an enlargement formed by the bulbocavernosus muscle. This is known as the bulbus urethræ. The walls of the spongy portion are thick and vascular and form the corpus cavernosum urethræ or corpus spongiosum. At its end the corpus cavernosum urethræ is greatly enlarged and forms the glans penis (m).
Glands of the Urethra.—1. The prostate ([Fig. 111], g) is a bilobed gland lying on the dorsal wall of the urethra and surrounding the ends of the vasa deferentia (c). It opens into the urethra at its beginning by numerous small ducts visible to the naked eye on the inner surface of the urethra.
2. The bulbourethral or Cowper’s glands ([Fig. 111], i).—There are two bulbourethral or Cowper’s glands, one on either side of the bulbus of the urethra between the ischiocavernosus and bulbocavernosus muscles. Each has a covering of muscle-fibres derived from the neighboring bulbocavernosus ([Fig. 113], l). Each is said to open by a single duct into the urethra at the root of the penis.
Fig. 111.—Male Genital Organs.
a, bladder; b, b′, ureters; c, vasa deferentia; d, spermatic cord; e, spermatic artery and vein; f, neck of bladder; g, prostate gland; h, urethra; i, bulbourethral (or Cowper’s) gland; j, corpus cavernosum penis, cut from ischium; k, ischiocavernosus muscle (cut); l, penis; m, glans penis; n, testis.
The penis ([Fig. 111], l; [Fig. 113], 6) is a cylindrical organ with the apex directed backward. It is covered by integument which projects at its free end in the form of a fold, the prepuce ([Fig. 113]), which ensheaths the glans ([Fig. 113], 7) of the penis. Beneath the integument is a layer of strong fibrous subcutaneous fascia continuous with that of the surrounding parts. On the dorsum of the penis a thin band of fibrous tissue, the ligamentum suspensorium penis, is continued from the middle line beneath the pelvic symphysis. This band divides distally, and its halves ensheath the glans and thus form a support of the penis.
The penis is formed by three bodies, the two corpora cavernosa penis and the single corpus cavernosum urethræ (corpus spongiosum).
The corpora cavernosa penis ([Fig. 111], j). Each is a cylindrical sheath of dense fibrous tissue within which are trabeculæ separating blood-sinuses. Each corpus cavernosum is attached by the one pointed end to the caudal border of the ramus of the ischium near the symphysis. From their attachments the corpora cavernosa approach one another, forming the crura of the penis. They become closely united by their medial surfaces and pass thus to the free end of the penis where their somewhat pointed distal ends are imbedded in the glans (m). A groove is left between the corpora cavernosa on the dorsum of the penis, and there is a second groove on the ventral side. In the latter groove lies the urethra.