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THE NEKVOUS SYSTEM. 



series. Each set comprises one of the two essential terminal parts of the sciatic 

 peroneal and tibial nerves and numerous smaller collateral branches. 



Anterior (Ventral) Branches. 

 Tibial nerve 

 Muscular branches 



Nerves to hamstring muscles 



quadratus femoris 



gemelli 



obturator internus 

 Articular branches (to hip-joint) 



Posterior (Dorsal) Branches. 

 Common peroneal nerve 

 Muscular branches 



Nerves to short head of biceps 



piriformis 

 Superior gluteal nerve 

 Inferior gluteal nerve 

 Articular branches (to knee-joint) 



NERVUS ISCHIADICUS. 



It has already been shown how the sciatic nerve is formed. It comprises the 

 two main nerves of the sacral plexus, bound together by an investing sheath, which 

 contains, in addition to the common peroneal and tibial nerves, a subordinate 

 branch of each, the nerve to the hamstring muscles, from the tibial, and the 

 nerve to the short head of the biceps femoris, from the peroneal nerve. A thick 

 band about half an inch in breadth is formed, consisting, from medial to lateral 

 side, of (1) nerves to the hamstring muscles, (2) tibial, (3) common peroneal, 

 (4) nerve to the short head of the biceps muscle. The sciatic nerve extends 

 through the buttock into the back of the thigh. Forming a continuation of the 

 sacral plexus, it enters the buttock by passing through the greater sciatic foramen, 

 in the interval between the piriformis and superior gemellus. Concealed by the 

 glutseus maximus muscle, it passes distally to the thigh, accompanied by the inferior 

 gluteal artery, and the arteria comitans nervi ischiadici. It lies in the hollow 

 between the greater trochanter of the femur and the tuberosity of the ischium, and 

 enters the thigh beneath the fold of the nates at the lower border of the glutseus 

 maximus. At that spot it is comparatively superficial, lying in the angle between 

 the edge of the glutseus maximus above and laterally, and the origins of the ham- 

 string muscles medially. In the thigh it is placed upon the adductor magnus, 

 anterior to the hamstring muscles, and it terminates at a variable point by dividing 

 into the tibial and common peroneal nerves. As already stated, these two nerves 

 may be separate from their origins, and their separation may occur at any point 

 between the greater sciatic foramen and the proximal part of the popliteal fossa. 



THE NERVES OF DISTRIBUTION FROM THE SACRAL PLEXUS. 



These are divisible into two series collateral and terminal branches. Each 

 subdivision consists of a series of anterior and posterior trunks. 



1. Collateral Branches. The anterior branches are (a) muscular branches (to 

 the quadratus femoris, gemelli, obturator internus, and hamstring muscles); and 

 (6) articular branches (to the hip-joint). These nerves all arise from the anterior 

 aspect of the sacral plexus. 



The nerve to the quadratus femoris (and inferior gemellus) arises from the 

 front of the fourth and fifth lumbar and first sacral nerves. It passes downwards 

 over the back of the capsule of the hip-joint (to which it sends a fine branch) beneath 

 the sacral plexus, gemelli, and obturator internus muscles. It supplies a nerve to 

 the inferior gemellus, and terminates in the deep surface of the quadratus femoris. 



The nerve to the obturator internus (and superior gemellus) arises from the 

 anterior aspect of the fifth lumbar and first two sacral nerves. In the buttock it 

 lies medial to the sciatic nerve on the lateral side of the pudendal vessels ; crossing 

 the ischial spine, it enters the ischio-rectal fossa through the lesser sciatic foramen. 

 The nerve supplies, in the buttock, a branch to the superior gemellus, and terminatee 

 by entering the pelvic surface of the obturator internus. 



The nerve to the hamstring muscles forms the most* medial part of the 

 sciatic trunk in the lower part of the buttock. It arises from all the roots of the 

 tibial nerve on their anterior aspect, viz., from the fourth and fifth lumbar anc 



