1332 



HUMAN ANATOMY. 



essential and frequently independent elements, the internal popliteal or tibial and the 

 external popliteal or peroneal. Typically the sciatic divides into these two nerves 

 in the lower part of the thigh ; very often, however, they are distinct from the outset, 

 arising independently from the plexus, being separated in the great sacro-sciatic fora- 

 men by the inferior fibres of the pyriformis muscle and passing through the thigh 

 as contiguous but ununited structures. Moreover, even when the sciatic appears to 

 be a single cord, dissection will reveal its duality in origin and course. The branches 

 of the sacral plexus may be grouped as follows : 



I. Collateral Branches. 



A. Anterior branches : 



1. Muscular 



2. Articular 



B. Posterior branches : 



3. Muscular 



4. Articular 



II. Terminal Branches. 



A. Anterior branch: 



5. External popliteal 



B. Posterior branch: 



6. Internal popliteal 



COLLATERAL BRANCHES. 



The collateral branches comprise two sets, designated according to the 

 portion of the plexus from which they arise as the anterior and the posterior. 



The anterior collateral branches include : (i) the muscular branches and 

 (2) the articular branches. 



FIG. 1113. 



Superior gluteal nerve, giving abr. to pyriformis 



Psoas magnus, cut 

 Ext. iliac artery 



Obturator nerve 



Pubic bone, 



mesial surface 



Obturator interims 



" White line" 9 



pelvic fascia 



Left corpus 



cavernosum, cut 



lir. to (|iiailratus 



fern., gemcllusinf. 



and hip joint 



Inf. gluteal 

 nerve 



Urethia 



Levator ani 



Anterior 

 crural nerve 



Coccygeus' 

 Br. to levator ani 



Nerve to obturator internus andgemellus superior 



' 



V. lumbar 

 vertebra 



V. lumbar nerve 



1. sacral 

 ganglion 



I. sacral nerve 



_Brs. to 

 pyriformis 

 II. sacral 

 ganglion 



. sacral nerve 

 Visceral hi. of 

 II. sacral nerve 



III. sacral 

 ganglion 



IV. sacral ganglion 

 (V. ganglion Is b< 



isceral brs. of III. and IV. sacral nerves 

 . sacral nerve (ventral division) 



toccygeal nerve (ventral division) 



Pudic nerve ; the small sciatic nerve is just in front 

 Br. to sphincter ani, piercing levutur am 



Dissection of right half of pelvis, showing sacral and pudenda! plexuses ; section is not meslai, 



but to left of mid-line. 



i. The muscular branches supply (a) the quadratus femoris, () the obtura- 

 tor internus, the gemelli and (c~) the hamstring muscles and the adductor magnus. 



a. The nerve to the quadratus femoris arises from the anterior surface of the upper portion 

 of the plexus, its fibres coming from the fourth and fifth lumbar and first sacral nerves. It is 

 ti. ( |n, ntl\ united in the first part of its course with the nerve to the obturator internus. Having 

 traversed the great sacro-sciatic foramen it courses downward anterior to the great sciatic nerve, 





