This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The normal prostate gland is of the shape of a large chestnut. It is 3 to 4 cm. (1 1/4 to 1 1/2 in.) wide, 2.5 to 3 cm. (1 to 1 1/4 in.) long, and 3 cm. (1 1/4 in.) thick. An indistinct furrow on its under surface separates it into two lateral lobes. There is no median lobe, as the prostatic tissue is continued uninterrupted across the median line. For clinical purposes we may consider the prostate as having an apex, a vesical surface or base, and a rectal or posterior surface.
The vesical surface is pierced a little anterior to its centre by the urethral opening, which leads to the apex. Entering below and posteriorly at the fissure are the ejaculatory ducts. These enter close together near the median line and pass upward and forward to enter the under surface of the prostatic urethra about its middle. It is to the part of the prostatic tissue between the ejaculatory ducts below and the interior of the bladder above, just posterior to the urethral orifice, that the name middle lobe has been applied. This part contains a collection of glands called by Albarran (Albarran and Motz: Annales des Mal. Genito- Urinaires, July, 1902) the prespermatic group. Just beneath the mucosa behind the urethra is another group which he calls the subcervical group. In so-called enlargements of the middle lobe these glands form the bulk of the tissue. A slight enlargement produces a bar, a considerable enlargement produces a projecting growth which may even be pedunculated. The glandular portion of the prostate in addition to that just described posterior to the urethral orifice is located centrally, and the fibromuscular part of the gland is mostly outside of the glandular portion, surrounding it and passing across the median line in front of the urethra to form the anterior commissure. Some fibres cross the median line posteriorly, forming an indistinct posterior commissure.
Fig. 454. - The prostate and its fascias.
The prostate is surrounded by a distinct firm fibrous sheath which is continuous with the rectovesical fascia (aporieurosis of Denon-villiers). At the upper portion this blends with the fascia covering the bladder, anteriorly it forms the puboprostatic ligaments, below it is continuous with the deep layer of the triangular ligament of the perineum, posteriorly it is continuous with the rectovesical fascia and covers and binds the seminal vesicles to the bladder. The prostatic plexus of veins is imbedded in this fibrous sheath. (J. W. Thomson Walker, Brit. Med. Jour., July 9, 1904.) (Fig. 454).
Between the veins and the glandular tissue, and covering the latter, is what has been called by Sir Henry Thompson and W. G. Richardson ("Development and Anatomy of the Prostate Gland") the capsule. It is a comparatively thin layer of fibrous tissue, insignificant and incomplete in places, which penetrates the substance of the gland. It adheres to and is removed with the lobes of the enlarged prostate in prostatectomy.
C. S. Wallace (Brit. Med. Jour., 1904, i., p. 239) holds that what Sir H. Thompson has called the capsule is the thin, muscular, outer, nonglandular portion of the organ. 29