ABDOMINAL CAVITY 551 



Dissection. To bring the anterior primary divisions of the lumbar 

 nerves into view, it is necessary to scrape away the psoas muscle. This 

 has already been partially done in following the connecting sympathetic 

 twigs backwards. An occasional branch, the accessory obturator, is liable 

 to injury unless it be secured at once. When present, it will be found 

 descending along the medial border of the psoas. 



Lumbar Nerves. The anterior primary divisions of the 

 lumbar nerves are five in number, and pass laterally in the 

 substance of the psoas muscle. They increase in size from 

 above downwards, and each nerve is joined by one or more 

 twigs from the sympathetic cord. Branches are given by 

 them to the psoas and quadratus lumborum muscles. 



The first three lumbar nerves, with a part of the fourth, 

 unite in a loop-like manner to form the lumbar plexus, whilst 

 the remaining part of the fourth joins the fifth to form the 

 lumbo-sacral cord. The fourth lumbar nerve is frequently 

 called the nervus furcalis, seeing that it enters into the forma- 

 tion of both the lumbar and sacral plexuses. 



Plexus Lumbalis (Lumbar Plexus). This plexus is placed in 

 front of the transverse processes of the lumbar vertebrae in the 

 substance of the psoas magnus. Above it is usually connected 

 with the last thoracic nerve by a small twig, which descends in 

 the substance of the psoas, to the first lumbar nerve ; below 

 it is brought into communication with the sacral plexus by 

 the branch of the fourth nerve, which enters into the forma- 

 tion of the lumbo-sacral cord. 



The following are the branches which proceed from the 

 lumbar plexus : 



3. Genito-femoral, 1st and 2nd lumbar nerves. 



4. Lateral cutaneous of thigh, ,, 2nd and 3rd lumbar nerves. 



5. Obturator, ,, 2nd, 3rd, and 4th lumbar nerves. 



6. Femoral, ,, 2nd, 3rd, and 4th lumbar nerves. 



7. Muscular branches to the quadratus lumborum and psoas magnus 



muscles which arise somewhat irregularly. 



The manner in which these nerves spring from the plexus 

 may now be studied. The first lumbar trunk breaks up into 

 three branches, viz. the ilio-hypogastric, the ilio-inguinal, and 

 the upper root of the genito-femoral. The second, third, and 

 fourth lumbar trunks each divide into an anterior and a 

 posterior division. The three anterior divisions are smaller 

 than the others, and they unite to form the obturator nerve ; 

 the three large posterior divisions unite to form the femoral 

 135 a 



