THE ABDOMEN 873 



glandular tissue. The chief part of the gland in front of the 

 urethra is composed of muscular tissue. The glandular element 

 consists of branched tubular alveoli or acini, the walls of which 

 are formed by a basement membrane, covered internally by 

 columnar epithehum. The tubular alveoli lead into the excretory 

 or prostatic ducts, the structure of which is similar to that of 

 the gland-tubes. The ducts average twenty in number, ten on 

 either side, and they open by independent orifices upon the posterior 

 wall of the prostatic portion of the urethra, for the most part into 

 the prostatic sinus on either side of the crest. 



Blood-supply — Arteries. — ^These are derived from the inferior 

 vesical, the middle hemorrhoidal, and the intrapelvic portion of the 

 sciatic. 



The veins form a copious prostatic plexus, which is most plenti- 

 ful over the anterior and lateral surfaces. It receives in front 

 the dorsal vein of the penis in two divisions, and discharges its 

 blood into the plexus which surrounds the neck of the bladder, 

 and thence by one or more vesical veins into the internal iliac vein. 

 The prostatic plexus is liable to become much enlarged in old age. 



Lymphatics. — These pass to the external iliac, internal iliac, sacral, 

 and common iliac glands. 



Nerves. — These are derived from the pelvic sympathetic plexus. 



Development. — ^The glandular part of the prostate is developed from the 

 epithelium of the uro-genital sinus. The epitheUal cells in the course of the 

 third month send out ramifying branches, which are at first solid, but subse- 

 quently become tubular, and so form the glandular part. 



Structure of the Rectum. 



The wall of the rectum is composed of five coats — serous, fascial, 

 muscular, submucous, and mucous. 



The serous coat is formed by the peritoneum, and, as has been 

 stated, is imperfect. 



The fascial coat represents a sheath which is derived from the 

 visceral pelvic fascia. In front of the rectum it is composed of 

 the recto-vesical and recto-prostatic laminae, whilst posteriorly it is 

 formed by the rectal lamina of that fascia. It is best marked over 

 the lower third of the rectum, where the peritoneimi is absent. 

 Elsewhere it is comparatively thin, and over the peritoneal area 

 it merges into the subperitoneal areolar tissue. 



The muscular coat is well developed, and is composed of plain 

 muscular tissue, arranged as an external longitudinal and internal 

 circular layer. The longitudinal layer is present all roimd the gut, 

 but attains its greatest development along the anterior and pos- 

 terior waUs, where it forms two broad stout laminae. Along the 

 sides it is somewhat sparse. The circular fibres form a continuous 

 covering for the rectum, and interiorly they become increased in 

 amoimt around the anal canal, and so give rise to the sphincter 

 ani internus. 



The submucous coat is composed of areolar tissue, and connects 



