THE LUMBAR NERVES 



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of the sacral plexus. The fourth nerve is named the nervus furcalis, from the fact 

 that it is subdivided between the two plexuses. 1 



The Lumbar Plexus 2 (plexus lumbalis) (Figs. 822, 823, 824). The lumbar plexuses 

 formed by the loops of communication between the anterior divisions of the first 

 three and the greater part of the fourth lumbar nerves; the first lumbar often 

 receives a branch from the last thoracic nerve. It is situated in the posterior part 

 of the Psoas major, in front of the transverse processes of the lumbar vertebrae. 



-From I2lh thoracic 



Iliohypogastric 

 llioinguinal 



Lot. femoral cutaneous 



To Psoas and 

 lliacus 



1st lumbar 



2nd lumbar 



rd lumbar 



lumbar 



5th lumbar 



Femoral 

 Accessory obturator 



Obturator 



Lumbosacral trunk 



FIG. 822. Plan of lumbar plexus. 



The mode in which the plexus is arranged varies in different subjects. It differs 

 from the brachial plexus in not forming an intricate interlacement, but the several 

 nerves of distribution arise from one or more of the spinal nerves, in the following 

 manner: the first lumbar nerve, frequently supplemented by a twig from the last 

 thoracic, splits into an upper and lower branch; the upper and larger branch divides 

 into the iliohypogastric and ilioinguinal nerves; tide lower and smaller branch 

 unites with a branch of the second lumbar to form the genitofemoral nerve. The 

 remainder of the second nerve, and the third and fourth nerves, divide into ventral 

 and dorsal divisions. The ventral division of the second unites with the ventral 

 divisions of the third and fourth nerves to form the obturator nerve. The dorsal 

 divisions of the second and third nerves divide into two branches, a smaller branch 

 from each uniting to form the lateral femoral cutaneous nerve, and a larger branch 

 from each joining with the dorsal division of the fourth nerve to form the femoral 



1 In most cases the fourth lumbar is the nervus furcalis; but this arrangement is frequently departed from. The 

 third is occasionally the lowest nerve which enters the lumbar plexus, giving at the same time some fibers to the sacral 

 plexus, and thus forming the nervus furcalis; or both the third and fourth may be furcal nerves. When this occurs, 

 the plexus is termed high or prefixed. More frequently the fifth nerve is divided between the lumbar and sacral plexuses, 

 and constitutes the nervus furcalis; and when this takes place, the plexus is distinguished as a low or postfixed plexus. 

 These variations necessarily produce corresponding modifications in the sacral plexus. 



2 Bardeen, Amer. Jour. Anat., 1907, vol. vi: 



