(Vas Deferens; Seminal Duct)
The ductus deferens, the excretory duct of the testis, is the continuation of the canal of the epididymis. Commencing at the lower part of the tail of the epididymis it is at first very tortuous, but gradually becoming less twisted it ascends along the posterior border of the testis and medial side of the epididymis, and, as a constituent of the spermatic cord, traverses the inguinal canal to the abdominal inguinal ring. Here it separates from the other structures of the cord. curves around the lateral side of the inferior epigastric artery, and ascends for about 2.5 cm. in front of the external iliac artery. It is next directed backward and slightly downward, and, crossing the external iliac vessels obliquely, enters the pelvic cavity, where it lies between the peritoneal membrane and the lateral wall of the pelvis, and descends on the medial side of the obliterated umbilical artery and the obturator nerve and vessels. It then crosses in front of the ureter, and, reaching the medial side of this tube, bends to form an acute angle, and runs medialward and slightly forward between the fundus of the bladder and the upper end of the seminal vesicle. Reaching the medial side of the seminal vesicle, it is directed downward and medialward in contact with it, gradually approaching the opposite ductus. Here it lies between the fundus of the bladder and the rectum, where it is enclosed, together with the seminal vesicle, in a sheath derived from the rectovesical portion of the fascia endopelvina. Lastly, it is directed downward to the base of the prostate, where it becomes greatly narrowed, and is joined at an acute angle by the duct of the seminal vesicle to form the ejaculatory duct, which traverses the prostate behind its middle lobe and opens into the prostatic portion of the urethra, close to the orifice of the prostatic utricle. The ductus deferens presents a hard and cord-like sensation to the fingers, and is of cylindrical form; its walls are dense, and its canal is extremely small. At the fundus of the bladder it becomes enlarged and tortuous, and this portion is termed the ampulla. A small triangular area of the fundus of the bladder, between the ductus deferentes laterally and the bottom of the rectovesical excavation of peritoneum above, is in contact with the rectum.
