DISSECTING MANUAL. 



parts of the lumbar and upper two sacral nerves unite to form 

 the peroneal nerve and posterior collateral branches. The 

 branches of the plexus are collateral and terminal, the latter 

 being the tibial and peroneal; all are divisible, according to 

 their origin, into anterior and posterior branches. [647] 



The great sciatic nerve consists of the tibial and peroneal 

 nerves, with the collateral branches to the hamstrings and 

 short head of the Biceps, all bound together in a sheath. It 

 descends with the sciatic artery under the Gluteus maximus, 

 between the ischial tuberosity and great trochanter, and then 

 upon the Adductor magnus, under the hamstrings; it divides 

 at a variable point in the thigh into the tibial and peroneal 

 nerves. The latter may be distinct from their origin, and even 

 separated by part of the Pyrif ormis ; in all cases they may be 

 artificially separated by removing the sheath. [648] 



Collateral Branches. Anterior series. 



The nerve to the Quadratus femoris arises from the front of 

 the fourth and fifth lumbar and first sacral nerves ; it descends 

 on the back of the hip-joint capsule, under the sacral plexus, 

 Gemelli, and Obturator internus, to enter the deep surface of 

 the muscle. It also supplies the Inferior gemellus. The nerve 

 to the Obturator internus arises from the front of the fifth lumbar 

 and first two sacral nerves and descends on the outer side of the 

 pudic vessels, below the great sciatic nerve ; then crossing the 

 ischial spine it runs through the lesser sciatic foramen to enter 

 the pelvic surface of the muscle. It supplies the Superior 

 gemellus also. [649] 



The nerve to the hamstrings arises from the roots of all the 

 nerves of the plexus, descends with the tibial nerve, and sepa- 

 rates into two sets of branches. The upper set passes inward 

 just below the ischial spine, to the upper part of the Semiten- 

 dinosus and the ischial head of the Biceps; the lower set leaves 

 the great sciatic (tibial) lower down and supplies the Semi- 

 membranosus, lower part of the Semitendinosus, and the Ad- 

 ductor magnus. Articular branches, to the hip, arise from the 



[284] 



