III

a. Remove now in front the deep layer of the superficial fascia of the PerinŠum, detaching it from the Pubic arch externally, and from the Triangular ligament behind. In doing this the distribution of the Perineal branch of the Pudic nerve may be with advantage traced. The fascia is seen to pass over the Transversus perinŠi muscle to join the Triangular ligament. The nerve will be found to divide into the following branches

1. The Posterior Superficial Perineal, which passes on the cutaneous surface of the Transversus muscle.

2. The Anterior Superficial PerinŠal, running beneath the Transversus muscle, and giving a transverse offset to the fore part of the Levator ani muscle.

3. Muscular branches, which may be traced to the Erector penis, Accelerator urinŠ, and Transrersus perinŠi muscles at once, and later on to the deep Transverse, and Constrictor urethrŠ muscles.

4. Slender twigs to the Corpus spongiosum.

The fascia investing the three superficial muscles may be now cleaned away.

4. Remove the Gluteus maximus muscle from its attachments internally to the Sacrum and Coccyx, and cut it through externally in a line parallel with the reflected skin. There will now be exposedŚ

In Front, The Anterior Triangle Of The PerinŠum, Bounded

Externally, by the Crus Penis with the Erector muscle lying upon it.

Internally, by the Bulb of the Corpus Spongiosum Urethra covered by the Accelerator urine muscle.

Posteriorly, by the Trans versus perinŠi muscle.

The Floor, formed by the Anterior layer of the Triangular ligament of the PerinŠum.

Under the Gluteus maximus muscle.

1. The Great Sacro-sciatic ligament passing between the sides of the Sacrum and Coccyx and the inner border of the Tuber Ischii. The Small Sacro-sciatic ligament crosses transversely beneath this from the side of the lower part of the Sacrum and the Coccyx to the Ischial spine.

2. The upper and posterior part of the Gluteus medius muscle is the highest of the structures displayed.

3. The Pyriformis muscle is next below, emerging from the great Sacro-sciatic foramen.

4. Next, the tendon of the Obturator internus muscle passing out from the lesser Sacro-sciatic foramen. It is overlapped here by the Gemelli muscles, the origins only of which are seen.

5. The Superficial branch of the Gluteal artery is seen between the Glutens medius and Pyriformis muscle with its accompanying vein, both however are divided at their point of entrance into the Gluteus maximus muscle.

6. The Sciatic vessels pass from the Pelvis below the Pyriformis muscle, and the Coccygeal branch is seen perforating the Great Sacro-sciatic ligament.

7. The Pudic vessels are seen upon the spine of the Ischium, with the Pudic nerve inside and the nerve to the Obturator internus muscle outside them.

8. The Great and Small Sciatic nerves, the Pudic nerve, the nerve to the Obturator internus muscle, the nerve to the Gemellus superior muscle, and the nerve to the Gemellus inferior and Quadratus fe-moris muscles are exposed passing from the Pelvis below the Pyriformis. The latter two, however, are here beneath the Great Sciatic nerve. Branches to the Gluteus maximus muscle from the Small Sciatic and Sacral plexus are also seen.

9. On the surface of the Great Sacro-sciatic ligament, the second series of loops between the external branches of the posterior primary divisions of the upper three Sacral nerves is seen. 10. A bursa over the Tuber Ischii is opened.

IV

a. Cut through in front the Superficial PerinŠal nerves and turn them forwards.

b. Detach the Crus Penis and Erector muscle from the Ramus of the Ischium and turn it inwards. This must be done carefully, to avoid injuring the Pudic artery, which lies between the Crus and the bone, but a branch which enters the Corpus Cavernosum at this point is unavoidably divided. The Pudic nerve is found here with the artery, and a similar branch from it to the Corpus Cavernosum is cut through.

c. Remove the Superficial Transversus perinŠi muscle.

d. Take away the Great Sacro-sciatic ligament, with the Coccygeal branch of the Sciatic artery, and the Sacral nerves.

e. Cut through the Pyriformis muscle at its point of emergence and turn it outwards.

f. Remove with the chisel the bone forming the inner portion of the upper part of the great Sacro-sciatic foramen, and the lower part of the Sacro-iliac articular surfaces, with the cartilage and ligaments in part. This is done to display the origin of the Pudic artery from the Internal Iliac trunk. There will now be exposedŚ

In The Perineal Region

1. The Anterior layer of the Triangular ligament.

2. The Pudic artery and nerve piercing it, and dividing into the branches for the Corpus Cavernosum, which are now cut, and the branches for the Dorsum of the Penis, which pass forwards to pierce the Suspensory ligament, the nerve lying outside.

The Anterior layer of the Triangular ligament may now be cleaned away, and the Pudic artery and nerve traced between the two layers. It will be found to give off a small transverse artery to the Bulb of the Corpus Spongiosum, which reaches that structure by perforating the Anterior layer of the ligament. There will now be exposedŚ

3. The Deep Transversus perinŠi muscle.

4. The Constrictor urethra muscle in front of the preceding, but usually continuous with it. The branches of nerve from the PerinŠal branch of the Pudic may now be traced to the preceding muscles.

In the Ischio-rectal regionŚ

The Pudic artery may be traced in the outer wall of the fossa.

In the Gluteal regionŚ

The Pudic artery may be followed from the Internal Iliac trunk in front of the lower end of the Sacral plexus, over the spine of the Ischium to the Ischio-rectal fossa. The Sciatic and Pudic veins must be removed to do this.

By the removal of the Pyriformis muscle, the following structures, in addition to those mentioned under Stage III., will be exposedŚ

1. Further portions of the Gluteal, and Sciatic arteries.

2. The first, second, third, and fourth Sacral nerves forming the plexus.

3. The first portion of the Gluteal nerve.

4. The nerves to the Pyriformis muscle from the upper and posterior part of the plexus.

5. The origin of the Pudic nerve, mainly from the third and fourth Sacral nerves.

6. The origin of the Small Sciatic nerve by two roots from the lower part of the plexus.