BRANCHES OF THE SACRAL PLEXUS. 



posterior divisions of the nerves, and thus the offsets of the plexus passing- to the limb may be 

 grouped as follows : 



Anterior or ventral nerve.*. l^oxterior or rfor.<ml tierces. 



Nerve to quadratus f emoris. Superior gluteal. 



Nerve to obturator internus. Inferior gluteal. 



Internal popliteal. Nerves to pyriformis. 



Small sciatic (perineal branch and inner External popliteal. 



part of femoral division). Small sciatic (gluteal branches and outer 



part of femoral division). 

 Perforating cutaneous. 



Varieties of the sacral plexus. The nerves proceeding from the sacral plexus vary in 

 their origin, like the offsets of the lumbar plexus, in accordance with the position of the 

 nernixfiircft.lix (see p. 313). The range of variation is shown in the following table, mainly 

 after Eisler : 



(The relative size of the several roots is indicated by the order of the nerves, and those 

 included in parentheses are inconstant.) 



A. COLLATERAL BRANCHES. 



Small muscular branches. The pyriformis muscle is supplied by twigs arising 

 from the back of the first angl second sacral nerves. 



The nerve of the quadratus f emoris muscle arises from the front of the upper part 

 of the plexus, receiving its fibres from the lumbo-sacral cord and first sacral nerve. 

 Concealed at first by the great sciatic nerve, it passes beneath the gemelli and the 

 tendon of the obturator internus between those muscles and the capsule of the 

 hip-joint, and reaches the deep (anterior) surface of the quadratus. It gives off a 

 branch to the inferior gemellus muscle, and another to the back part of the 

 hip-joint. A second filament frequently passes directly from the sacral plexus to the 

 articulation. 



The nerve of the obturator internus muscle, derived from the fifth lumbar and upper 

 two sacral nerves, springs from the front of the plexus immediately below the fore- 

 going, with which it is usually connected at its origin. Appearing at t ie lower 

 border of the pyriformis to the inner side of the great sciatic nerve, it then turns 

 over the ischial spine on the outer side of the pudic vessels, and is directed forwards 

 through the small sacro-sciatic foramen to reach the inner surface of the obturator 

 muscle. This nerve furnishes a small offset to the superior gemellus. 



Varieties. Occasionally the branch to the superior gemellus is also given off by the nerve 

 to the quadratus ; or that muscle may be supplied from both sources. In one instance 

 J. T. Wilson found the nerve to the quadratus continued to the upper part of the adductor 

 magnus (Journ. Anat., xxiii, 354). 



Superior gluteal nerve. The superior gluteal nerve arises from the back of 

 the lumbo-sacral cord and first sacral nerve. It leaves the pelvis with the gluteal 



