and composed of bone; behind, it is bounded by the sacrum and coccyx; whilst in front and laterally, it is bounded by the two ossa innominata. The bony wall, however, is deficient at certain points; thus, posteriorly, there is an interval on each side, between the sacrum and the os innominatum, which is partially filled up by the sacro-sciatic ligaments; again, laterally, there is the wide thyroid foramen, which is closed by the thyroid membrane; and, in front, there is the gap left by the pubic arch, which is occupied by the triangular ligament of the urethra.1

Upon the inner aspect of these boundaries of the pelvis there are placed certain muscles. Posteriorly, upon the anterior aspect of the sacrum, are the two pyriformes muscles; laterally, upon the inner aspect of each innominate bone, is the obturator internus muscle; whilst, in front, lying against the deep surface of the triangular ligament, is the compressor urethra muscle. But, in addition, there is a strong aponeurotic membrane, called the parietal layer of the pelvic fascia, which forms a complete lining for the pelvis, and is placed upon the deep surface of these muscles.

The pelvic wall may therefore be regarded as consisting of three strata, each composed of parts which lie in the same morphological plane, viz. :—

1. A bony, ligamentous, and membranous stratum.

2. A muscular stratum.

3. An aponeurotic stratum.

The pelvic cavity is closed below, and separated from the perineum by the visceral layer of the pelvic fascia, which passes inwards to the viscera from the parietal layer of the same aponeurosis, and also by the pelvic diaphragm, which is placed upon the under surface of the fascia. This diaphragm consists of the two levatores ani muscles and the

1 Let it be clearly understood that it is the inferior or superficial layer of the triangular ligament to which we refer, and not the "deep layer."

two coccygei muscles. The pelvic and abdominal cavities are directly continuous above and in front through the pelvic inlet.

The contents of the pelvic cavity differ in the two sexes; in both, however, the bladder occupies the fore part, and the rectum the back part of the space. The difference is to be found in the generative organs. It is necessary, therefore, to describe the male and female pelvis separately.

MALE PELVIS.

Within the male pelvis we find the following struc

tures:

Viscera.

1. The rectum.

2. The bladder, with the lower portion of the ureters, the prostate, and the prostatic portion of the urethra.

3. Vasa deferentia and the vesiculæ seminales. 1. The internal iliac vessels and their branches. 2. The superior hæmorrhoidal vessels.

Blood Vessels.

3.

The middle sacral vessels.

4.

Certain venous plexuses in connection with the viscera.

Nerves.

1. The sacral plexuses and their branches.
2. The obturator nerves.

3. The pelvic part of the sympathetic.

The peritoneum dips into the pelvis, and gives a partial covering to the rectum and the bladder.

General Position of Viscera.-The rectum occupies the posterior part of the cavity. It takes a curved course downwards upon the sacrum and coccyx, to the concavity of which a portion of it is adapted. The bladder is placed in the fore part of the cavity, and lies against the pubic bones. Behind the bladder, between it and the rectum, are the vesiculæ seminales and the vasa deferentia, whilst embracing its neck is the prostate. At present, however, the bladder and the rectum are the only viscera visible.

Peritoneum. The peritoneum is continued from the

Here it

posterior wall of the abdomen into the pelvis. comes into relation with the rectum, to which it gives a partial covering. The first part of the rectum it invests completely, and connects by means of a fold called the meso-rectum to the anterior surface of the sacrum. Gradually it leaves the gut, first disappearing from its posterior surface, then from its lateral, and finally from its anterior surface, and passes on to the lower and back part of the bladder. The point at which the peritoneum departs from

FIG. 135.-Side view of pelvic viscera. Subject in the
horizontal position.-(From WILSON'S Anatomy.)

the rectum may be stated to be about three inches above the anus, or, in other words, along a line connecting the middle points of the two vesiculæ seminales-somewhat less than an inch from the base of the prostate. This is a point, however, which is subject to variation. It is not uncommon to find the peritoneum passing lower down; and, in rare instances, it may even be seen to reach the base of the prostate before it is continued on to the bladder.

The peritoneum now ascends upon the back of the bladder, and, reaching its apex, is conducted from it by the urachus on to the posterior aspect of the anterior abdominal wall. On each side of the viscus it extends outwards as far as the obliterated hypogastric artery, along the line of which it quits the bladder, and is continued round the pelvic wall.

Recto-vesical Pouch.-As the peritoneum passes from the posterior wall of the pelvis to the back of the bladder, it is raised in the form of two semilunar ridges or folds by the obliterated hypogastric arteries. These folds extend forwards one on each side of the rectum, and they limit laterally a deep peritoneal pouch or recess between the rectum and bladder, which, from its position, is called the recto-vesical pouch.

False Ligaments of the Bladder.-Wherever the peritoneum leaves the bladder, to reach the pelvic or abdominal wall, it is termed "a false ligament." Of these, five are described-viz. two posterior, two lateral, and one superior.

The posterior false ligaments, or recto-vesical folds, are the two semilunar folds which limit the recto-vesical pouch laterally. They are produced, as we have seen, by the peritoneum being stretched over the obliterated hypogastric artery as it passes forwards to reach the bladder. Within each of these folds future dissection will reveal, in addition to the impervious hypogastric artery, the ureter and the superior vesical artery accompanied by some minute nerves.

The lateral false ligament is the name given to the peritoneum as it passes from each side of the bladder to the wall of the pelvis and the iliac fossa. This reflection has been seen to take place along the line of the obliterated hypogastric artery as it lies upon the lateral aspect of the bladder.

The superior false ligament is the portion of peritoneum which is continued from the summit of the bladder on to the posterior aspect of the anterior abdominal wall. It is led away from the viscus by the urachus and the two obliterated hypogastric arteries.

Hypogastric Nervous Plexus (plexus hypogastricus).— This is the lowest of the three great prevertebral plexuses, and is the main source from which the pelvic viscera are supplied with nerves. It is a dense flattened plexus, which lies in front of the body of the last lumbar vertebra in the interval between the two common iliac arteries. Superiorly, it is joined by numerous large filaments, which proceed downwards from the aortic plexus and the lumbar ganglia. Inferiorly, it ends by dividing into two lateral parts which are continued downwards on the back wall of the pelvis, and along the inner side of the internal iliac vessels to the pelvic plexuses.

Pelvic Fascia.-Now is the time to study the pelvic fascia, and it is a work which will require some care and patience on the part of the dissector. Much of the difficulty which is involved in the study of the pelvic fascia will be removed if the student will constantly keep before him two facts regarding it, viz., (1) That it constitutes a continuous lining for the inner surface of the pelvic wall. (2) That it sends across the pelvic cavity a layer which acts as a partition between the pelvis proper and the perineum. The lining-portion of the fascia may be termed the parietal part, and the partition-portion the visceral part. If the pelvis contained no viscera, the arrangement would be exceedingly simple, and might be represented diagrammatically as in Fig. 136.