A Dissection to Expose the Anterior Surface of the Sacral Plexus in the Male Subject. The Leg being removed, the Buttock and Perineum dissected, the Abdomen opened, and the viscera removed.
The body lying on its back.
The first step will be to make a side view of the Pelvis, and to do this the following steps are necessary on the side on which the section is to be made. The plexus of the opposite side is the one that is to be exposed.
a. Remove the Psoas muscle and the External Iliac vessels along the brim, and part of the Iliacus muscle from the Venter Ilii.
b. Dissect off the Pelvic fascia from the brim of the Pelvis. This is to be done carefully keeping close to the bone, and thus taking away the Obturator internus muscle, and the dissection should be carried nearly as far forwards as the Symphysis, backwards to the fascia of the Pyriformis, and as low down as possible.
c. Separate the Obturator fascia, with the falciform process of the Great Sciatic ligament, and the Obturator muscle, from the outer wall of the Ischio-rectal fossa. This incision will meet the above.
d. Saw off the spine of the Ischium.
e. Saw through the Rami of the Pubis and Ischium, an inch external to the Symphysis Pubis.
f. Saw through the Innominate bone behind, the incision extending from the outer margin of the Quadratus lumborum above, vertically downwards to the great Sacro-sciatic foramen. Or the bone may be disarticulated behind, by removing the Multifldus and Erector spinæ muscles from the Sacro-vertebral groove, dividing the Anterior and Posterior Sacro-iliac, the mo-lumbar, Lumbo-sacral, and Great Sciatic ligaments, and forcibly separating the bones. In this way the Auricular cartilage which adheres to the Sacrum mostly, may be displayed.
g. When the bone is removed, the spine of the Ischium should be fixed down, and the Obturator internus muscle-gently peeled off the outer surface of the Pelvic fascia, when the following will be exposed—
1. The Pelvic fascia, and white line extending from the lower part of the Symphysis to the Ischial spine.
2. The Obturator fascia below this line.
3. The Obturator nerve, artery, and vein, running transversely above, in this order from above downwards, and passing out in front through the opening above the Obturator membrane. They lie in the substance of the Pelvic fascia.
The Pudic vessels, and nerve, are seen lying in the substance of the Obturator fascia, or rather in a sheath derived from its inner surface. They may be traced backwards round the Ischial spine, and as far forwards as the Triangular ligament.1
Remove now the Obturator fascia at the white line. Divide the Anal fascia along this line; cut through the origin of the Levator ani muscle from it, and expose the Recto-vesical fascia2 running downwards and inwards to the viscera. Below it are the following parts closing the Pelvic outlet from before backwards:—
1 A good dissection of the Pudic artery may be made in this way, but the anterior' section of the bone would have to be modified.
2 The above is the account of the arrangement of the Pelvic fascia as usually given. It is, however, frequently found, that the Pelvic fascia is directly continuous with the Recto-vesical, and the white line is formed by the upper edge of the Obturator, which is loosely connected with the Pelvic by areolar tissue. The origin of the Levator ani muscle often extends considerably above the white line.
1. The Triangular ligament.
2. The Levator ani muscle.
3. The Coccygeus muscle, and the smaller Sacro-sciatic ligament.
4. The Great and Small Sciatic nerves, the Pudic nerve, the nerve to the Obturator internus muscle.
5. The Sciatic vessels, piercing the fascia of the Pyriformis.
The preceding vessels and nerves leave the Pelvis below the Pyriformis muscle.
6. The Pyriformis muscle.
7. The Sacral plexus lying upon it, and giving off the above-named branches.
8. The Gluteal vessels and nerve, above the Pyriformis muscle, and piercing the fascia over it.
a. Cut away the Recto-vesical fascia and its prolongations to the viscera on the side of the Pelvic section, the Pubo-prostatic ligament, and Ellis's ligament of the Rectum.
b. Remove the piece of Peritoneum passing to the viscera from the side of the Pelvis on which the section has been made, and display in this way a side view of the Pelvic viscera.1 The following are the parts now seen—
1. The divided portions of the Innominate bone.
2. The Rectum in the concavity of the Sacrum and Coccyx ; most posteriorly branches of the Superior Hæmorrhoidal artery may be seen in removing the sheath of Recto-vesical fascia. Owing to the curvature of this viscus to the left, a better view is obtained by making the section on this side.
1 To show the parts more clearly, the Bladder should be inflated through the Ureter, and the Rectum filled with tow.
3. The Bladder in front of the preceding.
4. The Recto-vesical pouch of Peritoneum between the Bladder and Rectum.
5. The Prostate gland surrounding the neck of the Bladder, and enveloped by the Prostatic plexus of veins, the sheath of the Recto-vesical fascia being removed.
6. In front of the preceding the two layers of the Triangular ligament perforated by the Membranous Urethra, and in front of the ligament the Bulb.
7. Between the Fundus of the Bladder and the Rectum the Vesicula Seminalis of the side dissected.
8. The Ureter is seen descending internally to the Internal Iliac vessels, and entering the posterior and external part of the Fundus of the Bladder.
9. The obliterated Hypogastric artery is seen running transversely on the upper part of the side of the Bladder to the apex, and continuous behind with the Internal Iliac artery.
10. Crossing over the immediately preceding structure, and running vertically down internally to it and the Ureter, is the Vas Deferens, accompanied by its artery.
11. Extending from the apex of the Bladder on to the Abdominal wall are the Urachus, and both obliterated Hypogastric arteries.
12. Extending from the Abdomen over the Sacro-iliac Synchondrosis the Internal Iliac artery. Its Obturator, Sciatic, and Pudic branches are divided, as well as the Gluteal, but the Superior, Middle, and Inferior Vesical offsets are seen, the former giving the branch to the Vas, and the Middle very inconstant. The Middle Hæmorrhoidal artery is also displayed, commonly arising from the Inferior Vesical or the Pudic branches.
13. The corresponding veins. These are plexiform at their origin, and form the Prostatic, Vesical, and Hæmorrhoidal plexuses, which are found on the sides of the corresponding viscera. The Dorsal vein of the Penis is seen entering the Prostatic plexus.
14. The Pelvic plexus of the Sympathetic nerve of the side dissected is seen surrounding the Iliac vessels, and sending prolongations to the viscera along the vessels.
15. Lymphatic glands along the Iliac vessels.
16. Below these structures are seen the parts closing the outlet of the Pelvis already enumerated above.
Divide now the following structures— a. The Spermatic cord at the internal Abdominal ring of the side on which the section has been made.
b. The obliterated Hypogastric artery.
c. The Ureter.
d. The Vesical and Middle Hæmorrhoidal arteries and veins of the side dissected.
e. Cut through the Meso-rectum, containing the Superior Hæmorrhoidal artery and vein, and the accompanying Sympathetic plexus, and draw the Rectum well over to the side from which the bone has been removed. f. Strip off the Peritoneum passing from the Bladder and Rectum to the opposite side of the Pelvis.
g. Divide the obliterated Hypogastric artery, the Spermatic cord, the Vesical and Hæmorrhoidal vessels, and the Ureter of the opposite side.
A. Cut through the Recto-vesical fascia of the opposite side at its visceral attachments, and pull the Bladder over to the same side as the Rectum.
i. Dissect out the Internal Iliac vessels and their branches, and remove them; except the Obturator, which may remain on the Pelvic wall. These branches have already been enumerated. In cleaning these the other Pelvic Sympathetic plexus will be destroyed.
j. Remove the fascia of the Pyriformis. There will now be exposed—
1. The anterior surfaces of the Sacrum and the Coccyx and the posterior surface of the Symphysis Pubis.
2. Lying on the Sacrum, the Sacra Media and Lateral Sacral arteries and veins. The Hypogastric Sympathetic plexus, and the gangliated cords of the Sympathetic, one on each side, are seen uniting below in the ganglion impar. The Coccygeal gland may be found below this, receiving branches from the ganglion impar and the Sacra Media artery.
3. The Psoas muscle, External Iliac vessels, and Pelvic wall of the opposite side, and covering the wall:—
4. The Pelvic fascia lining the Obturator interims muscle; below is the white line, and below this the Recto-vesical fascia covering the Levator ani muscle. The Recto-vesical fascia may be seen closing the Pelvis in front, leaving in the median line a little triangular interval between the Pubic attachments of the Levatores ani; here it is very thin, and dips down to join the Prostatic capsule. This fascia is seen to be separated from the Triangular ligament by the Levatores ani muscles.
5. The Obturator nerve, artery, and vein are seen running across the Pelvic wall in this order from above downwards. Behind the Symphysis are the Pubic branches of the Obturator, and Deep Epigastric arteries.
6. The Coccygeus muscle behind the Levator ani muscle, passing from the sides of the Sacrum and Coccyx to the Ischial spine.
7. The Sacral plexus consisting of the Lumbo-sacral cord, and the first, second, third, and part of the fourth nerves, their communications with the Sympathetic ganglia and the following branches. The Gluteal, arising from the posterior part of the Lumbosacral cord, and the first or first two Sacral nerves. The nerve to the Obturator internus muscle derived from the front of the plexus at the union of the Lumbo-sacral cord, with the first Sacral nerve. Visceral branches to the Bladder and Vagina, from the second, third, and fourth nerves (Godlee). Ellis describes them as coming from the fourth nerve, and sometimes from the third. In this dissection they came from the second, third, and fourth.
8. The remainder of the fourth nerve, its Hæmorrhoidal branch, which is seen passing over the Coccygeus muscle and turning to the back of the Coccyx, between that muscle and the Levator ani, or perforating the former. The branch to the visceral surface of the Levator ani muscle, which also supplies the Coccygeus. This is internal to the preceding, and is seen by dissecting off the Rectovesical fascia from the Levator ani muscle. 9. The nerve formed by the united anterior primary branches of the fourth, fifth, and the Coccygeal, perforating the Coccygeus muscle to be distributed to its posterior surface.