In the echidna and ornithorynchus, amongst the Monotremata, there is a gland on each side of the cloaca, small, and of an oval shape, containing within it a central canal opening into an excretory duct : this pene trates the constrictor cloacm, and joins a small seminal canal detached from the urethra, near its termination in the cloaca. The gland is surrounded by a thick muscle, the action of which is forcibly to throw forwards the fluid along the long excretory canal with which it is provided.
Cowper's glands are altogether wanting in birds. They are not found in reptiles gene rally ; but in the amphibious Urodeles the genitourinary opening is surrounded by a glandular apparatus in some respects ana logous. In fishes they are wanting.
They belong to the class of glands desig nated by Cuvier as supplementary to the male organs of generation, and their use is to pour out a fluid to lubricate the spongy portion of the urethra, and by blending with the seminal and other fluids, to assist in the general distension of the canal.
Bloodvessels of the Urethra.— The urethra is a highly vascular membrane, and its arteries are derived on either side from that branch of the pudic which enters the corpus spongiosum at the bulb, and is known by the name of the arteria corporis spongiosi urethrce vel arteria bulbi. This artery divides into small branches, many of which are distributed on the cells of the corpus spongiosum, whilst others pass through this body, and penetrating the elastic tunic of the urethra are distributed upon its mucous sur face, forming intricate plexuses between and at the basis of its columns : others are des tined to the lacunae over which they form a delicate network, which conveys to these crypts a cellular appearance. They all freely anastomose on the general surface of the urethra, and at the meatus communicate with those minute branches of the arteria dorsalis penis, which, having reached the prepuce, are reflected over the cutaneous surface of the glans penis.
The veins either communicate with those of the spongy body, and empty themselves into the dorsal vein of the penis, or terminate at once in the prostatic plexus by means of those already described in the membranous portion.
Nerves. — The nerves are exceedingly small ; they accompany the arteries of the bulb, but cannot be traced into the urethral membrane, although the high sensibility of this structure even in health, and especially under disease, indicates at once a considerable nervous supply. The nerves are derived partly from the pudic nerves, which give minute branches, taking the course of the arteries of the bulb, and partly from the plexus situated beneath the neck of the blad der formed by some small branches of the sacral nerves and sacral ganglion of the sym pathetic.
The lymphatics — join the superficial and deep lymphatics of the penis, and either ter minate in the inguinal glands, or, passing into the pelvis with the pudic vessels, join the ganglion situated around the internal iliac artery.
Function. — The office of the urethra is to give exit to the urine from the bladder, and the secretions of the testes and their ap pendages the vesiculm seminales, the prostate and Cowper's glands. For the free discharge of the urine, the urethra is in a passive con dition, and the penis relaxed, and as free as possible of blood ; the muscles surrounding the membranous portion together with the slightly resisting urethra yield to the eflorts of the detrusor urinm, and the urine passes in a stream varying in size and force ac cording to the condition of the canal. If any obstruction exists either at the prostatic part, or in any other situation, the force, size, shape, or direction, of the urinary stream is altered according to circumstances; and hence, by inspection during the passage of the urine, we can often arrive at a satisfactory conclu sion of the nature of the obstruction without the introduction of instruments.
When, however, the seminal secretion is to be expelled, the condition of the urethra is totally altered, and the canal is diminished in diameter hut increased in length from the general distension of the penis with blood, and the consequent erection of the organ. The direction of the anterior part of the urethra is altered and straightened to the utmost ; the prostatic part is raised by the action of the levator prostates', and thus forms a gentle inclination with the membranous part; and the fluid oozing through the vasa ejaculatoria is collected in the bulb, which thus becomes distended. Although it is not possible to see what is going on, yet we may - imagine that at this period of the orgasm a sort of vermicular movement takes place, and that successive contractions and relaxations of the muscular apparatus of this part of the genitourinary system occur. Thus I appre hend that the sphincter vesice effectually closes up the orifice of the bladder, whilst the levator ani and compressor prostate ex pel the contents of the vesiculm and the pro state : and further, that after the bulb is dis tended with fluid, the acceleratores urine con tract with considerable and successive effort, and at this moment the muscles surrounding the membranous part contracting prevent any retrogression-of the seminal and vesicular se cretions, and thus the contents of the urethra are forcibly expelled through the anterior part of the canal, now made rigid by the distension of the penis, and by the contraction of its own peculiar tissue, a forcible muscular effort being required to expel the somewhat inspissated fluids. The erection of the caput gallinaginis, by the distension of its erectile tissue, has considerable influence in closing up the prostatic part of the urethra, and thus assists in preventing its retrogression into the bladder.
The action of the acceleratores urine• in expelling the contents of the urethra in the venereal orgasm, has been denied on the high authority of Cuvier. Kobelt believes that their sole action is to compress the bulb, and thus to force the blood onwards into the glans penis, and to increase the turgescence of this body ; but that they have no direct influence either in accelerating the flow of urine as their name implies, or in the evacua tion of the urethra during the act of copu lation.* There are few parts with which the consti tution has a more close sympathy than the urethra : this is evinced by the general disturb ance of health tinder the influence of diseases of this canal : thus, in inflammation from gonorrhoea, or even common causes, irritative fever is set up, persisting frequently as long as the disease lasts. So also, when in suspected or actual stricture, a bungle is passed along the canal, faintness occurs, followed by a class of symptoms resembling those of the suc cessive stages of an ordinary intermittent. When ulceration takes place, a similar train of symptoms sets in. The same is also fre quently remarked during the passage of stones, or fragments of stone, along the canal. This sympathy must be referred to the general nervous supply derived from the filaments of the sympathetic and cerebrospinal axis. The sensibility of the urethra is not the same throughout ; it is evidently more intense at the commencement, in the prostatic and nieni branous portions, and near the meatus, than in the spongy part generally. The pain, how ever, accompanying diseases of the urethra is commonly referred to the meatus, in obedi ence to the well-known law, that when irrita tion of any of the mucous surfaces produces pain, this is principally felt at the point where the mucous and cutaneous systems blend into one another, namely at the outlet of the mucous canal.