1332 



HUMAN ANATOMY. 



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

 external popliteal at 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 : — 



II. Terminal Branches. 



A. Anterior branch: 



5. External popliteal 



B. Posterior branch: 



6. Internal popliteal 



I. Collateral Branches. 



A. Anterior branches : 



1. Muscular 



2. Articular 



B. Posterior branches : 



3. Muscular 



4. Articular 



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. II 13. 



Superior gluteal nerve, giving a br. to pyriformis Nen-e to obturator internus and gemellus superior 



Anterior ': 



crural nerve 



Psoas magnus, cut 

 Ext. iliac artery 



Obturator nerve 



Pubic bone. 



mesial surface 



Obturator internus 



"White line" of 



pelvic fascia 



Left corpus 



cavernosum, cut 



Br. to quadratu^ 



feiu., gemellus inf. 



and hip join; 



Inf. gluteal 



nerve 



Coccygeus 

 Br. to levator ani 



. lumbar 

 vertebra 



. lumbar nerve 



I. .sacral 

 ganglion 



I. sacral nerve 



.-Brs. to 

 pyriformis 



II. sacral 

 ganglion 

 II. sacral nerve 

 visceral br. of 

 II. sacral nerve 



III. sacral 



ganglion 

 IV. sacral ganglion 

 (V, ganglion is seen below) 



isceral brs. of 111. and IV. sacral nerves 

 'V. sacral nerve (ventral division) 



'Coccygeal nerve (ventral division) 



Pudic nerve : the small sciatic nerve is just in front 

 Br. to sphincter ani, piercing levator am 



Dissection of right half of pelvis, showing sacral and pudendal plexuses ; section is not meslat, 



but to left of mid-line. 



I. The muscular branches supply (a) the quadratus femoris, {b') 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 

 frequently 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, 



