Hunter, and most of his successors, believe the matter of gonorrhoea to be incubated in the lacuna magna.
Structure.— The urethral membrane is divi sible into two distinct layers. The inner, which is analogous to other mucous surfaces, consists of a basement membrane covered throughout by epithelium. This, according to Quain and Sharpey, for the most part, is of the scaly character, but in the vicinity of the bladder it is spheroidal. Ilenle describes the fossa navicularis as covered with small flat and roundish scales, whilst the remaining part of the urethra is covered with a single series of prismatic particles.* Beneath the mucous membrane there is a layer composed of a tissue or structure of a mixed character, containing some contractile fibres, supposed to be muscular, blended with elastic tissue. It is connected to the delicate tendinous covering of the corpus spongiosum, and is supported by transverse tendinous bands distinctly visible beneath it. This layer varies in depth in different parts, and is thicker in the membranous than in other parts of the urethra. When examined with the micro scope, it presents abundant evidence of the existence of contractile fibre mixed with com mon elastic tissue. The relative quantity of these elements varies according to situation : thus, in the membranous portion, there is less of the contractile tissue than in the spongy portion ; a circumstance of some interest, as, this part being surrounded by a distinct mus cular covering, there would be less necessity for it than in other situations where muscle is absent. The bloodvessels from the spongy body shoot through it. This contractile tissue is identical with that recently described by Kiilliker as entering into the structure of the spleen and mucous canals, which have an evidently contractile power.
The existence of this layer has been long recognised, and the attention of anatomists was directed specially to it by Sir E. Home, who believed it to be muscular ; and his opinion was supported by the observations of Mr. Wilson, who attributes the resist ance occasionally, in irritable states of the urethra, offered to the introduction of the catheter, and the expulsion of bougies in like conditions, to spasm of these supposed mus cular fibres. This idea, however, was opposed by Sir Charles Bell ; but the dispute is de prived of its interest since the discovery by Kolliker of the true nature of this peculiar tissue, which combines to a certain extent the attributes of organic muscular fibre and elastic tissue. This layer varies in depth in different
subjects, and is generally highly developed in the robust and muscular, so as in some in dividuals to grasp with considerable firmness a bougie when introduced into the canal. Wilson mentions an instance of a gentleman who could "as distinctly feel a contraction of the passage coming on, and taking place at one part, as he could feel any muscle act." The use of this layer must necessarily be to regulate the force of the current of fluids through the urethra.
According to Kolliker the following is the arrangement of the submucous layer in various parts of the urethra. It is termed by him the simple muscular tissue. " Its relations are most complicated in the prostate gland, and the prostatic portion of the urethra, which is rich in muscular fibres. So large is the quantity of this tissue in the gland itself, that the true glandular structure constitutes scarcely one third or one fourth of the whole. On removing the mucous membrane from the prostatic portion of the urethra, the yellow longitudinal fibres of the caput gallinaginis come first into view, which form the lower end of the trigone, and contain very few mus cular fibres. On both sides of the caput gal linaginis, and extending to the anterior wall of the urethra, similar yellowish longitudinal fibres present themselves, and form a strong layer towards the neck of the bladder; but towards the membranous part of the urethra they gradually decrease to a very delicate layer. This longitudinal fibrous layer of the prostatic part is connected, internally to the sphincter vesicte, by a thin and indistinct layer of fibres with some of the longitudinal mus cular fibres of the bladder ; but by far the greater part of it is unconnected with this latter : it consists of half fibro-cellular tissue with many nucleus-fibres, and half of evident, smooth, muscular fibres with characteristic nuclei. After this, and external to it, follows, secondly a strong layer of yellowish circular, fibres of muscular and elastic tissue. This layer is connected above with the sphincter vesicm, where also it is most developed ; whilst below it becomes gradually thinner, and below the caput gallinaginis is either lost, or appears only in very small quantities. On removing the several muscular layers, we come at last to the proper glandular tissue of the prostate, of which individual lobes penetrate among the circular fibres just mentioned, their ex cretory through the longitudinal fibres.