SACRAL PLEXUS-ANTERIOR RAMI BRANCHES (BEFORE DIVISION)

SUMMARY

6 Ps
1. S1 + 2 => Piriformis nerve. 

2. S2 + 3 => Perforating cutaneous nerve - pierces the sacrotuberous ligament to supply a small portion of skin over the medial side of the buttock.
3. S2 + 3 => Posterior femoral cutaneous nerve - runs below the piriformis on the sciatic nerve (it lies on the fascia lata which separates it from the sciatic nerve). It runs as far as the lower ends of the gastroc bellies and supplies an area of skin b/w the anterior and posterior axial lines from buttock to mid-calf. Gives off gluteal and perineal branches. 

4. S2 + 3 + 4 => Pelvic splanchnic nerves - constitute the sacral parasympathetic outflow. 
5. S2 + 3 + 4 => Pudendal nerve - runs down and curves around the coccygeus muscle to enter the pudendal canal. 
6. S2 + 3 + 4 => Perineal branch of the pudendal nerve - sensory to the posterior 2/3 of the scrotum/labium, motor to the muscles of the urogenital triangle. 

Reference(s)

R.M.H McMinn (1998). Last’s anatomy: regional and applied. Edinburgh: Churchill Livingstone.
Gray, H., Carter, H.V. and Davidson, G. (2017). Gray’s anatomy. London: Arcturus.