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. The ducts of Cowper's glands open by very minute orifices on the sides of the spongy urethra anterior to and near the bulb. On the floor of the prostatic urethra appears the crest of the veru montanum, upon which the two seminal ducts open by orifices directed forwards. On either side of the veru montanum the floor of the prostate may be seen perforated by the "excretory ducts" of this so-called gland. The part K, which is here represented as projecting from the floor of the bladder, near its neck, is named the "uvula vesicae," (Lieutaud.) It is the same as that which is named the "third lobe of the prostate," (Home.) The part does not appear as proper to the bladder in the healthy condition, Fig. 2, Plate 56.