THE LUMBAR PLEXUS 



999 



from the last thoracic nerve, as it is in about 50 per cent, of the cases, and it thus 

 contains fibres of both the last thoracic and the first lumbar nerves. It pierces 

 the lateral border of the psoas and crosses in front of the quadratus lumborum 

 (fig. 765), and behind the kidney and the colon. At the lateral border of the 

 quadratus it pierces the aponeurosis of origin of the transversus abdominis and 

 enters the areolar tissue between the transversus and the internal oblique, where 

 it frequently communicates with the last thoracic and with the ilio-inguinal 



Fig. 764. — Diagram of a Common Form of Lumbo-sacral Plexus. (Modified from 



Paterson.) 

 From last thoracic nerve » 



'^-"'•""Firs*' lumbar 



Genito-femoral 

 Ilio -hypogastric 

 Ilio-inguinal'— 



Lateral cutaneou 



Obturator-.. 

 Accessory obturator... 



--"•Second lumbar 



-—Third lumbar 



Fourth lumbar 



---•Fifth lumbar 



First sacral 



Second sacral 



Third sacral 



Visceral branches 



Fourth sacral 



Visceral branches 



Perineal 



Fifth sacral 

 To coccygeus 

 To levator ani 

 Coccygeal 



Common j,..,. 

 peroneal &V;i' 

 section - "'" 



Tibial 



section 



To hamstrings 



To obturator internus 



Posterior femora] 

 cutaneous 



Ano -coccygeal 



nerve, and it divides into an iliac and a hypogastric branch, which correspond, 

 respectively, with the lateral and anterior branches of a typical spinal nerve. 



The anterior cutaneous (hypogastric) branch passes forward and downward, between the 

 transversus abdominis and the internal oblique muscles, giving branches to both; it communi- 

 cates with the ilio-inguinal nerve, and, near the anterior superior spine of the ilium, it pierces 

 the internal oblique muscle and continues forward beneath the external obUque aponeurosis 

 toward the middle line. About 2.-5 cm. (1 in.) above the subcutaneous inguinal ring it pierces 

 the aponeurosis of the external obUque, becomes subcutaneous, and supplies the skin above the 

 symphysis. 



The lateral cutaneous (iliac) branch pierces the internal and external obUque muscles, 

 ernerging through the latter above the iliac crest at the junction of its anterior and middle 

 thirds (fig. 769). It is distributed to the integument of the upper and lateral part of the thigh, 

 in the neighborhood of the gluteus medius and tensor fasciae latse muscles (fig. 768). 



