SECTION XVI 



LUMBAR AND SACRAL PLEXUS AND NERVES OF 

 LOWER LIMB 



THE anterior divisions of the remaining spinal nerves viz., five 

 lumbar, five sacral, and one coccygeal form the lumbo-sacral 

 plexus, which supplies the lower part of the trunk and the lower 

 limb. For convenience of description the plexus is divided into 

 three parts lumbar, sacral or sciatic, and pudendal. 



The lumbar plexus is formed by the first four lumbar nerves 

 and a branch of the twelfth thoracic. 



The sacral or sciatic plexus is formed by part of the fourth 

 lumbar, the fifth lumbar, and the first three sacral nerves. 



The pudendal plexus is formed by branches from the second 

 and third sacral nerves, the fourth and fifth sacral nerves, and 

 the coccygeal nerve. This plexus supplies mainly the perineum. 



The Lumbar Plexus is formed by the anterior divisions of the 

 first three lumbar nerves, a part of the fourth, and a small 

 branch from the twelfth thoracic nerve. It is placed deeply in 

 the substance of psoas just in front of the transverse processes 

 of the lumbar vertebrae. On emerging from the intervertebral 

 foramina, and after communicating with the sympathetic system, 

 the nerves divide to form the plexus. 



The first and second nerves divide into upper and lower parts. 

 The upper part of the first nerve joins with the branch from the 

 twelfth thoracic and forms the ilio-inguinal and ilio-hypogastric 

 nerves. The lower part of the first nerve and the upper part of 

 the second join to form the genito-crural nerve. The lower part 

 of the second nerve, the third nerve, and the upper part of 

 the fourth nerve divide into anterior and posterior parts. The 

 anterior parts join to form the obturator nerve, and the posterior 

 parts form the anterior crural nerve ; from the posterior parts of 



192 



