In the membranous part of the urethra the smooth muscular tissue is less developed. Under the mucous membrane, whose cellular tissue is remarkable for abundance of elastic fibres, there is a layer of longitudinal fibres, which are connected with those of the pro static portion. These fibres consist for the most part of fibro-cellular tissue with nucleus fibres, and include, in small numbers, undulating, delicate, and curved contracting fibre-cells (of the nature of smooth muscular fibres), which may be, in part, isolated ; and are from to of a line long, from 1.002 to 0.003 wide. They contain small nuclei from 0.012 to 0.014. long, and are more easily found in recent specimens than in those treated with acetic acid. External to these longitudinal fibres there is a strong layer of transverse fibres, which belong for the most part to the mus cuhts urethralis. Some of these, however, especially those belonging to the inner layer, display some strong bundles of smooth mus cular fibres, together with fibro-cellular tissue and nucleus-fibres, and a partial mixture of fasciculi of the transversely striated fibres of the musculus urethralis.
The smooth muscular fibres are generally still less developed in the spongy portion of the urethra. In some cases they appear in exactly the same manner as the longitudinal fibres in the membranous portion ; in other cases, longitudinal fibres may be seen, but no muscular tissue can be found mingled with the cellular tissue and nucleus-fibres of which they consist. At a certain depth, however some longitudinal fibres are distinguishable, with a more or less considerable admixture of smooth muscle, which fibres cannot be re garded as beams of the corpus cavernosum urethra; (corpus spongiosum), since they have no venous spaces between them, but rather form a continuous membrane, which limits the corpus cavernosum urethra: towards the mucous membrane. One might con sider this part as belonging to the corpus cavernosum urethrae ; in which point of view we shall deny any muscular membrane to this region of the urethra: but it seems more na tural to regard the whole corpus cavernosunz as a highly developed muscular layer provided with peculiar bloodvessels ; for a large quan tity of smooth muscular fibres, together with the cellular tissue, vessels, and nerves, en tering into the structure of its beams and cords as far as the glans, render this body an eminently contractile structure."* On laying open the urethra from its origin at the neck of the badder, the first structure we meet with is the caput gallinaginis (colli culus seminalis, caruncula senzinalis, veru mon tanum, crista urethrce). This is an elongated body situated on the floor of the prostatic part of the urethra : it varies in length from three quarters of an inch to an inch. Com mencing by a gentle elevation of the urethra, towards which, on either side, are seen some delicate folds of membrane passing, it expands into a small oblong rounded eminence, com pared to the head of a woodcock, and hence its name : it then advances gradually, tapering to a slender point, which, being continued onwards for some distance, is lost at the beginning of the membranous portion in one or two delicate longitudinal folds, and is con founded with the general surface of the urethra : the latter part is compared to the beak of the bird. The caput gallinaginis di vides the prostatic sinus into two lateral de pressions, into which the secretion of the prostate gland is poured.
At the most elevated portion of the caput gallinaginis there is a depression formed by an inflexion of mucous membrane, facing for wards, variable in size and depth, and gene rally capable of admitting the blunt end of an ordinary probe : in some cases it can be traced down beneath the third lobe of the prostate, to the extent of the third, or even the half, of an inch. It is called the sinus pocu
laris, utriculus prostaticus, or vesica prostatica, and is the homologue of the protometra, from which the female uterus is evolved.t On either side of this, between its laminm, or beneath it, are the terminations of the ejacu latory ducts. A general description of this small cavity has been given under the head of PROSTATE GLAND.
The structure of the caput gallinaginis is this : it is for the most part formed of a raised fold of the ordinary mucous membrane of the urethra, beneath which is a longitudinal layer of elastic tissue continuous with the trigone. Some anatomists also affirm that there is mixed up in the tissue of the body a plexus of vessels, constituting a distinct erectile tissue ; and hence it has been ima gined, that when its vessels are distended with blood, as during erection of the penis, it shuts up the prostatic portion of the urethra, and thus prevents the passage of the semen in a retrograde direction into the bladder. My own opinion as to its use is, that, independent of this office, it is endowed with special sensi bility, like the papillary orifices of the ducts of Steno and Wharton ; and that it is capable, under the influence of a stimulus, of becom ing erect, and thus straightening the termina tion of the canals connected with it, by which the exit of the secretion of the testes and vesiculac scminales is favoured. I believe, further, that something more is due to these papillary orifices of the ducts of glands, and that, in consequence of their exquisite sensi bility and sympathy with the glands, they possess a power, under stimulation, of elicit ing the secretion and expulsion of the fluid of the bodies with which they are connected. A proof of its sensibility may be deduced from the fact, that when a bougie, introduced for the first time per urethrazzz, reaches this point of the canal, it frequently gives rise to faint ness and sickness ; and this is usually attended with an almost irresistible desire to micturate ; and further, that if this be frequently re peated, and the caput gallinaginis be irritated, a flow of semen and vesicular secretion can be excited.
The pathology of this portion of the canal leads to the same conclusion. For the relief of nocturnal emissions, so frequently the result of repeated self-pollution, the prxternatural irritability of this part may be successfully destroyed by the application of the nitrate of silver.
If the caput gallinaginis be gently raised by dissection from the subjacent tissue, it will be found lying on a delicate tendinous layer, with which it is intimately connected. This layer in shape resembles the body itself, being broader behind and tapering in front, and is gradually confounded with the tendinous covering of the spongy body: it is also continuous with the fascial layer of the utriculus prostaticus.
The caput gallinaginis results in a great measure from the coalition of the two lateral portions of the urethra, during the develop ment of the back part of the canal, from that portion of the uro-genital sinus which gives origin to the prostate and vesiculte semi nales, &c.
In the membranous portion there is nothing specially remarkable, except that delicate venous plexus, to which allusion has been already made. In the bulbous part are the terminations of the ducts of Cowper's glands ; and to these bodies I shall now direct attention.