Ans. b (Posterior portion of psoas) (Ref. BDC anatomy Vol. II 3rd ed., 278)LUMBAR PLEXUS# The lumbar plexus lies in the posterior part of the substance of the PSOAS MAJOR muscle.# It is formed by the ventral rami of the upper 4 lumbar nerves.Its branches include:- Ilioinguinal nerve (L1)- Lateral cutaneous nerve of the thigh (L2, L3 dorsal divisions)- Lumbosacral trunk (L4, 5; ventral trunk)- Genitofemoral nerve (L1, L2, ventral divisions)- Obturator nerve (L2, 3, 4; dorsal divisions)- Femoral nerve (L2, 3, 4; dorsal divisions)- Iliohypogastric nerve (L1)Branches of the lumbar plexusNerveSegmentMuscleMotionSensationIliohypogastricT12 -L1# Inter oblique# External oblique# Transversus abdominusAnterior abdominal wall# Inferior abdominal wall# Upper lateral quadrant of buttockIlioinguinalL1Internal obliqueAnterior abdominal wall# Internal medial inguinal ligament# GenitaliaGenitofemoralL1-L2CremasterTesticular# Inferior medial inguinal ligament# Spermatic cordLateral femoral cutaneousL2-L3 # Anterior, lateral and posterior aspect of thighFemoral Nerve1. Anterior division L2-L4# Sartorius,# Pectineus# Medial aspect of lower thigh# Adduction of thigh# Anterior medial skin of thigh2. Posterior division Quadriceps# Knee extension# Patellar movement# Anterior thigh hip and kneeObturator nerve1. Anterior division L2-L4# Gracilis# Adductor longus# Adductor brevis# PectineusThigh adduction# Posterior medial thigh# Medial knee# Hip2. Posterior division # Adductor magnus# Obturator externusThigh adduction with lateral hip rotationKnee