422 



LUMBAR PLEXUS. 



LUMBAR. NERVES. 



There are five pairs of lumbar nerves, of which the first makes its ap- 

 pearance between the first and second lumbar vertebras, and the last be- 

 tween the fifth lumbar and the base of the sacrum. The anterior branches 

 increase in size from above downwards. They communicate at their ori- 

 gin with the lumbar ganglia of the sympathetic, and pass obliquely out- 

 wards behind the psoas magnus or between its fasciculi, sending twigs to 

 that muscle and to the quadratus lumborum. In this situation each nerve 

 divides into two branches, a superior branch which ascends to form a loop 

 of communication with the nerve above, and an inferior branch which 

 descends to join in like manner the nerve below, the communications and 

 anastomoses which are thus established constituting the lumbar plexus. 



The posterior branches diminish in size from above downwards ; they 

 pass backwards between the transverse processes of the corresponding 

 vertebrae, and each nerve divides into an internal and an external branch. 

 The internal branch, the smaller of the two, passes inwards to be distri- 

 buted to the multifidus spinse and interspinales, and becoming cutaneous 

 supplies the integument of the lumbar region on the middle line. The 

 external branches communicate with each other by several loops, and after 



supplying the deeper muscles, 



Fi - 189 -* pierce the sacro-lumbalis to reach 



the integument to which they are 

 distributed. The external branches 

 of the three lower lumbar nerves 

 (nervi clunium superiores postici) 

 descend over the superior part of 

 the crest of the ilium, and are dis- 

 tributed to the integument of the 

 gluteal region. 



LUMBAR PLEXUS. 



The Lumbar plexus is formed 

 by the communications and anas- 

 tomoses which take place between 

 the anterior branches of the five 

 lumbar nerves, and between the 

 latter and the last dorsal. It is 

 narrow above and increases in 

 breadth inferiorly, and is situated 

 between the transverse processes 

 of the lumbar vertebrae and the 

 quadratus lumborum behind, and 

 the psoas magnus muscle in front. 



* A view of the lumbar and ischiatic plexus and the branches of the former. 14. 

 The bodies of the lumbar vertebrae. 13. The psoas magnus muscle. 11. The iliacus 

 jnternus muscle. 15. The quadratus lumborum muscle. 16. The diaphragm. 12. The 

 three broad muscles of the abdomen. 17. The sartorius. 1. The lumbar plexus. 2. 

 The ischiatic plexus. 3, 3. Abdomino-crural nerves. 4. External cutaneous nerve 

 (inguino-cutaneous). 5, 6, 7. Cutaneous branches from (8) The anterior crural nerve. 

 U. The genito-crural nerve or spermaticus externus. 10, 10. The lower termination of 

 the great sympathetic. 



