thra
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 obstacl