THE LUMBAR PLEXUS 165 



compressed against the superior crus (pillar) of the ring by 

 large inguinal herniae and give rise to painful symptoms. 



The Genito-femoral Nerve arises from the first and second 

 lumbar nerves, and descends on the surface of the psoas major. 

 It divides into the lumbo-inguinal (femoral brancti) and the 

 external spermatic nerves (genital branch). The former varies 

 considerably in size. Usually, it supplies a small area of 

 skin just distal to the middle of the inguinal ligament (of 

 Poupart), but occasionally it extends as far as the knee, 

 supplying a large area of skin on the front of the thigh. 



The external spermatic nerve enters the spermatic cord 

 and supplies the cremaster muscle, which constitutes one of 

 the coverings of the cord and testis. In addition, it supplies 

 a sensory branch to the tunica vaginalis testis (p. 375) 

 (iMackenzie). 



The Cremaster Muscle is derived from the lower border 

 of the internal oblique and it consists of a number of muscular 

 loops, of varying size, which pass downwards on the spermatic 

 cord and then ascend to the inguinal ligament (of Poupart). 

 When the muscle contracts, it drags the testis upwards 

 towards the subcutaneous inguinal ring. 



The cremasteric reflex depends on the integrity of the 

 genito-femoral nerve and the segments of the spinal medulla 

 from which it arises. When the skin of the proximal part 

 of the front of the thigh is lightly stroked, the testis is drawn 

 upwards in the scrotum. This reflex is particularly active in 

 children, but it is not so easy to elicit in the adult. The 

 afferent impulse passes along the lumbo-inguinal nerve and 

 reaches the second lumbar segment of the spinal medulla. 

 From there, the efferent impulse is conveyed to the cremaster 

 muscle by the external spermatic nerve. The cremasteric 

 reflex is increased in lesions of the spinal medulla above the 

 second lumbar segment. 



The Lateral Cutaneous Nerve of the Thigh arises from the 

 second and third lumbar nerves. After emerging from the 

 psoas major, it crosses the iliacus and reaches the lateral 



