The prostatic portion of the urethra has received attention in con nection with the anatomy of the prostate. The principal diseases of this part of the canal have also received consideration as prostatic rather than urethral affections. While the urethra is under normal circumstances a urinary organ, it is by no means necessary to the function of micturition. It is, however, quite necessary to the pro creative act. The urethra is, therefore, a sexual rather than a uri nary organ.
The length of the urethra as given by most anatomists is from eight to nine inches, but the greatest discrepancy exists upon this particular point. A table showing the estimates of various clinical observers would show a marked variance of opinion. A difference of from twenty to thirty per cent. in the estimated measurements of equally competent observers is not unusual, and is hardly to be won tiered at. It is probable that no two observers can possibly obtain precisely similar conditions for measurement. The penis varies in size not only intrinsically in different subjects, but there is the greatest imaginable variation in the same subject under different psychological conditions. The same conditions affect the calibre of the canal.
The individual urethra is a law unto itself as far as its length is concerned. The length of a particular urethra may be said to be the distance from the meatus traversed by the catheter before the urine begins to flow, the penis being flaccid and placed upon a degree of tension merely sufficient to afford adequate support during instru mentation. Due allowance should be made for sexual excitation or emotional inhibition.
The anterior curve of the urethra is not of great importance with relation to instrumentation, as it can be adapted to almost any form of instrument. It is different, however, with the posterior or deep
curve, which is relatively fixed; it cannot be said to be constantly fixed, for, as is well known, straight instruments can be intro - duced into the bladder. The fixed urethral curve is not uniform, but varies widely with the period of life and the condition of the prostate body. It is comparatively short and sharp in the child, much longer and less abrupt in the adult, these characteristics greatly in creasing in prominence as the subject grows older. In prostatic en largements the curve becomes so greatly elongated as to necessitate considerable modification of instruments and in manipulations for en tering the bladder. This point is of the greatest practical impor tance to the genito-urinary surgeon. The direction and conforma tion of the pendulous urethra may be modified by changes in the position of the penis. It may also be adapted to any form of instru ment necessary for urethral or bladder manipulation.
The average normal curve as established by Bell, and verified by Thompson, Van Buren, and others, corresponds to a circle three and one-fourth inches in diameter, the proper length of curve for adapta tion to the deep urethra being an arc of such a circle subtended by a chord two and three-fourths inches in length. The length of curve, as outlined by Thompson, is generally too long for instruments. The shorter the beak of the sound—providing it be adapted to the normal curve—the more thoroughly under control will the instrument be during instrumentation.