The colour of the mucous membrane de pends on the degreee of vascularity in dif ferent parts. Thus, at the meatus, it is of a pink aspect, becoming gradually pale towards the bladder. But in the membranous por tion, owing to congestion in the veins, it is very frequently much darker, as these vessels are readily distinguishable through the mem brane, whilst in the prostatic part it is white. The colour of the mucous membrane is much heightened under inflammation: this is espe cially visible in the fossa navicularis, and at the orifice in severe attacks of gonorrhoea; and the same has been witnessed in other parts of the canal after division of the urethra, during an attack of gonorrhoea. Under in flammation it loses its smooth, polished aspect, and presents a velvety appearance.
Mr. Quekett has lately made some beautiful injections of the vessels of the mucous mem brane of the urethra, in which it is seen that, in the bulbous portion, the bloodvessels run ning in the valleculie between the columns are larger and more numerous than those of the columns themselves; whilst nearer the meatus, where the columns are either small or alto gether absent, the membrane is not unfre quently provided with villi, which resemble those of the lips and extremities of the fingers and toes in having each a single looped capil lary.
Lacuna.. — The whole of the urethra, ex cept the prostatic portion, is marked by minute openings, distinctly perceptible at the upper and under surface, but they are certainly larger and more numerous on the upper. They are the openings of the lacunae or mucous glands, whose office it is to secrete a bland fluid for the lubrication of the canal, and thus to facili tate the onward progress of the contents of the urethra. The lacuna vary in different individuals in size and number : some anato mists believe them to be more numerous in the membranous portion : my own observa tions would lead me to the conclusion, that the greater number are to be found in the spongy portion. They are termed indiscrimi nately the glands of Littre and Morgagni, or the orifices are called the lacuna of Morgagni, whilst the crypts opening into them are termed glands of Littre. The lacuna vary in depth : in some situations they admit the passage of bristles, to the depth of two or three lines; in others they are by no means so deep, whilst in other cases they are scarcely perceptible. Their orifices face for the most part obliquely forwards towards the meatus, but now and then they pass vertically to the surface ; they are found between and upon the columns of the urethra. A simple examination of the
lacuna would represent them as mere in flexions of the mucous membrane of the urethra, and many of the smaller ones are of this nature : some, however, present a cellular appearance, but this seems to arise from the anastomosis of vessels distributed on them : they are lined with epithelium of a character similar to that lining the urethral membrane generally, and a considerable plexus of vessels is distributed around them. Under inflamma tion they pour out a copious secretion, and are not unfrequently the seat of special disease. The use of the lacuna is to extend the secret ing surface of the mucous membrane of the urethra, in situations where any glandular ap paratus would have been obviously incon venient.
In old cases of stricture, and other diseases of the canal, they become exceedingly enlarged.
The lacuna magna. — Near the termina tion of the urethra, and within a few lines of the meatus urinarius, will be seen an inflexion of the urethral membrane, forming a cul-de-sac, into which the bunt end of a probe can be passed : this is denominated the lacuna magna, being in structure and function analogous to the other lacuna of the urethra. The lacuna magna is a point in the anatomy of the urethra of some practical import, inasmuch as it is likely to arrest the entrance of a catheter, and to convey to the ignorant an erroneous idea of stricture. It varies in situation in different individuals. It is usually placed at about one-third of an inch from the meatus on the dorsal aspect of the fossa navicularis, so that, on separating the lips of the meatus, it can be brought into view; but it is occa sionally further back, and now and then is placed on the under surface, and in many cases I have in vain tried to find it. I believe it is occasionally altogether absent. It will be found, where the columns of the urethra are developed, that they take their course towards the lacuna, and, on reaching it, pass off in slender processes to the meatus. In an urethra which I recently examined, I found a lacuna magna of considerable size in the under surface of the urethra, behind the middle of the spongy body. Into this the point of a catheter could be readily passed, and it might have been easily mistaken for stricture.