The central part of this canal is lined by a very vas cular and sensible mucous membrane, between which and the spongy body of the urethra there are several longitudinal cavities, called lacume, opening within the urethra, and serving as excretory ducts to the mucus with which this canal is moistened. Dr Barclay has lately observed a number of cells running longitudinally, but rather in a serpentine direction, between the mem brane and the spongy body, so as to have the appearance of irregular vessels, or canals, which seem to commu nicate laterally, and might be filled with air or mercury from the orifices of the /acume.—See Edin. /lied. and Surg. Jour. vol. i. p. 4U3.
We have mentioned numerous ducts opening into the urethra at its origin, within the neck of the bladder, viz. two front the seminal vesicles and visa deftrentia, and ten or twelve from the prostate gland. Besides these there are usually other ducts opening into the bulb of this canal, and coming from two small bodies of a glan dular structure, situated at the distal extremity of the bulb, on the sides of the peripheral surface of the mem branous part of the urethra, and called, from their dis coverer, Cowper's glands.
Many important changes take place in the reproduc tive organs of man during his progress through life. This is particularly the case with the testes ; the situa tion and relations of which are very different in the foetus, from those of the same organs after birth.
From the time when they are first perceived till about the eighth month of pregnancy, the testes of the fcetus are lodged within the belly, one in each lumbar region, a little sacrad of the kidneys, and resting on the psoce muscles by the sides of the rectum. Here they are closely enveloped by that doubling of the peritoneum, which is to become their future tunice albuginea. Be tween the testes, in this situation, and that part of the scrotum to which the cremaster muscle is attached, there extends, on each side, a ligamentous cellular and vascular cord, of a conical form, called by Mr John Hunter the gubernaculum, or ligament of the testes. At this period the two cavities of the scrotum, in which the testes are to be lodged, are separated from the of the pelvis by portions of the peritoneum, that just dip within the cavities of the scrotum.
Generally about the eighth month of pregnancy, or a few weeks previous to parturition, the testes begin to change their situation, and to pass very gradually sa crad towards the scrotum.t The manner in which this
passage of the testes takes place, is not yet perfectly understood, though it has attracted the attention of some of the ablest anatomists and physiologists of modern times. In particular, the investigations of Haller, John Hunter, Camper, and Wrisberg, have contributed to improve our knowledge of this singular phenomenon in the animal economy ; but their investigations have done little more than explain to us the exact situation of the testes, and their connection with the neighbouring parts at different periods of their passage. Mr Hunter sup posed, that the principal agent in promoting the pas sage of the testes into the scrotum is the conical cord, which he therefore called gubernaculum, or helm ; but it does not appear that the action of these bodies could bring the testes further than to the abdominal ring.
As the testes advance through the abdominal rings into the scrotum, they push before them those doublings of the peritoneum, which we described as dipping within the scrotal cavities ; and these doublings now heroine the vaginal coats of the testes. When the testes first pass into the scrotum, there is an opening left between the cavity of the vaginal coat and that of the pelvis. Hence it may, and sometimes does happen, that a por tion of the intestines slips through the abdwinnal ring into the scrotum along with the testes, funning that modification of hernia or rupture, called congenital. alter the testes have passed into the scrotum, however, a firm adhesion generally takes place between the vagi nal and albugineous coats, thus obliterating the commu nication between the belly and scrotum.
We have described the passage of the testes into the scrotum as usually taking place about the eighth month of pregnancy. In some cases, however, they have been found within the scrotum so early as the third or fourth mouth ; and it not unfrequently happens, that they du not descend till some months, or even years, after birth. This is said to be very common among the inhabitants of Hungary. (Roux in Ilichat's Azatoniie Descript. tent. v. p. 253.) Sometimes only one enters the scrotum, and, in a new rare cases, they remain altogether w ithin the belly.