Plate 55--Figure 2

COMMENTARY ON PLATES 54, 55, & 56. 123

Fig. 3, Plate 55.--The membranous urethra A is also in some instances embraced by two symmetrical fasciculi of muscular fibres B B, which arising from the posterior and lower part of the symphysis pubis, de­scend on either side of the canal and join beneath it. The muscles B C, Fig. 2, Plate 55, are between the two layers of the deep perinaeal fascia, while the muscle B B, Fig. 3, Plate 55, lies like the forepart of the leva­tor ani, C C, behind this structure and between it and the anterior ligaments of the bladder. [Footnote] As to the interpretation of the muscle, I, myself, am inclined to believe that it is simply a part of the levator ani, and for these reasons--1st, it arises from the pubic sym­physis, and is inserted into the perinaeal median line with the levator ani; 2nd, the fibres of both muscles overlie the forepart of the prostate, and present the same arrangement in parallel order; 3rd, the one is not naturally separable from the other.

[Footnote: This is the muscle, B B, which is described by Santorini as the "levator prostatae;" by Winslow as "le prostatique supe­rieur;" by Wilson as the "pubo-urethrales;" by Muller as not existing; by Mr. Guthrie as forming (when existing), with the parts B C, Fig. 2, Plate 55, his "compressor isthmi urethrae;" and by M. Cruveilhier as being part of the levator ani muscle. "As in one case," (observes Mr. Quain,) "I myself saw a few vertical muscular fibres connected with the transverse com­pressor, it has been thought best to retain the muscle in the text."--Dr. Quain's Anat., Am. Ed. vol. ii. p. 539.]

Plate 55--Figure 3

Fig. 1, Plate 56, represents by section the natural forms of the urethra and bladder. The general direc­tion of the urethra measured during its relaxed state from the vesical orifice to the glans is usually described as having the form of the letter S laid procumbent to the right side [capital S rotated 90 degrees right] or to the left [capital S rotated 90 degrees left]. But as the ante­rior half of the canal is moveable, and liable thereby to obliterate the general form, while the posterior half is fixed, I shall direct attention to the latter half chiefly, since upon its peculiar form and relative position depends most of the difficulty in the performance of catheterism. The portion of the urethra which in­tervenes between the neck of the bladder, K, and the point E, where the penis is suspended from the front of the symphysis pubis by the suspensory ligament, assumes very nearly the form of a semicircle, whose anterior half looks towards the forepart, and whose posterior half is turned to the back of the pubis. The pubic arch, A, spans crossways, the middle of this part of the urethra, G, opposite the bulb H. The two ex­tremes, F K, of this curve, and the lower part of the symphysis pubis, occupy in the adult the same antero-­posterior level; and it follows, therefore, that the dis­tance to which the urethra near its bulb, H, is removed from the pubic symphysis above must equal the depth of its own curve, which measures about an inch per­pendicularly. The urethral aperture of the triangular ligament appears removed at this distance below the pubic symphysis, and that portion of the canal which lies behind the ligament, and ascends obliquely back­wards and upwards to the vesical orifice on a level with the symphysis pubis in the adult should be re­membered, as varying both in direction and length in individuals of the extremes of age. In the young, this variation is owing to the usual high position of the bladder in the pelvis, whilst in the old it may be caused by an enlarged state of the prostate. The curve of the urethra now described is permanent in all positions of the body, while that portion of the canal anterior to the point F, which is free, relaxed, and moveable, can by traction towards the umbilicus be made to continue in the direction of the fixed curve F K, and this is the general form which the urethra assumes when a bent catheter of ordinary shape is passed along the canal into the bladder. The length of the urethra varies at different ages and in different individuals, and its structure in the relaxed state is so very dilatable that it is not possible to estimate the width of its canal with fixed accuracy. As a general rule, the urethra is much more dilatable, and capable consequently of receiving an instrument of much larger bore in the aged than in the adult.

The three portions into which the urethra is de­scribed as being divisible, are the spongy, the mem­branous, and the prostatic. These names indicate the difference in the structure of each part. The spongy portion is the longest of the three, and extending from the glans to the bulb may be said on a rough, but for practical purposes, a sufficiently accurate estimate to comprise seven parts of the whole urethra, which measures nine. The membranous and prostatic por­tions measure respectively one part of the whole. These relative proportions of the three parts are main­tained in different individuals of the same age, and in the same individual at different ages. The spongy part occupies the inferior groove formed between the two united corpora cavernosa of the penis, and is sub­cutaneous as far back as the scrotum under the pubes, between which point and the bulb it becomes embraced by the accelerator urinae muscle. The bulb and glans are expansions or enlargements of the spongy texture, and do not affect the calibre of the canal. When the spongy texture becomes injected with blood, the canal is rendered much narrower than otherwise. The canal of the urethra is uniform-cylindrical. The meatus is the narrowest part of it, and the prostatic part is the widest. At the point of junction between the mem­branous and spongy portions behind the bulb, the canal is described as being naturally constricted. Be­hind the meatus exists a dilatation (fossa navicularis), and opposite the bulb another (sinus of the bulb). Muscular fibres are said to enter into the structure of the urethra, but whether such be the case or not, it is at least very certain that they never prove an obstacle to the passage of instruments, or form the variety of stricture known as spasmodic. The urethra is lined by a delicate mucous membrane presenting longitudi­nal folds, which become obliterated by distention; and its entire surface is numerously studded with the ori­fices of mucous cells (lacunae), one of which, larger than the rest, appears on the upper side of the canal near the meatus. Some of these lacunae are nearly an inch long, and all of them open in an oblique direc­tion forwards. Instruments having very narrow apices are liable to enter these ducts and to make false pas­sages.