CHAPTER VII 



THE NERVES 



THE LUMBO-SACRAL PLEXUS 



This is the name given to the great fasciculus from which the nerves 

 which supply the hind limb are derived. In its formation it presents 

 great similarity to the plexus from which the nerve-supply of the fore 

 limb is derived — namely, the brachial plexus, which was described in 

 Vol. II. 



The plexus may be said to be made up of anterior and posterior 

 divisions, each united to the other by a thick connecting trunk. To 

 the formation of the plexus the inferior primary divisions of the fourth, 

 fifth, and sixth lumbar and the first and second sacral nerves contribute. 

 There is also a slender contribution from the third lumbar nerve. Each 

 root is named from the vertebra which forms the anterior boundary 

 of the intervertebral foramen through which it emerges. The slender 

 branch from the third sacral nerve unites with the contribution from the 

 fourth, which is also slender. The trunk thus formed passes backwards, 

 and is joined by a much thicker contribution from the fifth lumbar. 

 Thus is formed what we have termed the anterior division of the plexus. 

 Two large nerves — the anterior crural and obturator — are detached 

 from the fasciculus, which thus becomes very much reduced in size 

 and passes backwards as the trunk referred to as connecting this portion 

 with the posterior division. This trunk, together with much larger 

 contributions from the sixth lumbar and the first and second sacral 

 nerves, forms an enormous flat fasciculus, from which the anterior and 



