7.1 Anal Triangle

Question 1

Describe the region of the anal and urogenital triangles

Answer 1

Perineum is a diamond-shaped area between the legs.
Anal triangle is inferior.
Urogenital triangle is anterior.

Question 2

Describe the pudendal canal.

What is contained within the pudendal canal?

Answer 2

• The fascial sleeve on the obturator internus’s medial surface
• Internal pudendal vessels and pudendal nerve.

Question 3

Identify the internal pudendal artery and vein.
From where does the artery branch?
Where does the vein drain?

Answer 3

• Internal pudendal artery is an anterior branch from the internal iliac a.
• Internal pudendal vein drains into internal iliac v.

Question 4

Identify the pudendal n.

From where/what plexus does it branch? Describe its course and what regions it innervates.

Answer 4

• Anterior division of Sacral Plexus (S2-S4).
• Exits pelvis via greater sciatic foramen, enters perineum via lesser sciatic foramen.
• Supplies skin and muscles of perineum; main sensory nerve for external genitalia.

Question 5

Identify the levator ani muscles.

What 3 muscles make up the levator ani, what is their course and function, and what are they innervated by?

Answer 5

The levator ani has three parts: (medial-lateral)

1. The puborectalis, which originates from the superior pubic rami on both sides of the pubic symphysis and inserts onto the anococcygeal ligament.
2. The pubococcygeus, which originates from the pubis, lateral to the origin of the puborectalis, and inserts onto the anococcygeal ligament and coccyx.
3. The iliococcygeus, which originates from the tendinous arch of the levator ani and inserts onto the anococcygeal ligament and coccyx.

• Innervation: Sacral plexus (S4), inferior anal nerve.
• Function: Act to lift the anal canal. Help form diaphragm and support pelvic viscera (rectum and anal canal).

Question 6

Identify the external anal sphincter, its attachments/function, and innervation.

Answer 6

• The external anal sphincter encircles the anus, running posteriorly from the perineal body to the anococcygeal ligament.
• Innervation: Pudendal nerve (S2 to S4).
• The external anal sphincter is tonically active, so inhibition causes relaxation.

Question 7

Describe the anococcygeal ligament and its attachments..

Answer 7

A fibrous median raphe in the floor of the pelvis, which extends between the coccyx and the margin of the anus.
Composed of fibers of the levator ani, external anal sphincter, and fibrous CT.

Question 8

Identify the inferior rectal artery, vein, and nerve. Describe the course and function for each.

Answer 8

• These all arise/drain from internal pudendal artery/vein/nerve and are distributed among the anal region.
• The inferior rectal aa. anastomose with the corresponding vessels of the opposite side, with the superior and middle rectal arteries, and with the perineal artery.