DISSECTION OP THE DOG 85 



In its course the sciatic nerve lies in succession on the deep gluteal muscle, 

 the tendon of the internal obturator, the gemelli, .the quadratus femoris, the 

 adductor and (possibly) the semimembranosus muscles. It is covered by the 

 piriformis, middle gluteal and biceps ; and the abductor posterior crosses it 

 obliquely in the proximal third of the thigh. As it curves round the region 

 of the hip-joint the nerve lies on the oral side of the caudal gluteal vessels. 



The branches of the sciatic nerve are as follows : (1) A branch arising before 

 the sciatic leaves the pelvis, and dividing into twigs for the piriformis, internal 

 obturator, and gemelli muscles; (2) nerves to the biceps, semitendinosus, 

 semimembranosus, and quadratus femoris muscles. These leave the sciatic 

 in the form of a large common trunk, springing from the parent nerve on a 

 level with the highest part of the trochanter major ; (3) a small nerve to the 

 posterior abductor muscle of the leg ; (4) lateral cutaneous nerve of the leg 

 (n. cutaneus surse lateralis). The two last-named branches leave the sciatic 

 about the same point, this varying from just beyond the trochanter major 

 to about the middle of the thigh. If the sciatic nerve divides unusually early, 

 the nerves to the abductor and the cutaneous nerve are branches of the common 

 peroneal nerve. The cutaneous nerve gains the leg by running between the 

 semimembranosus, semitendinosus, and abductor muscles medially and the 

 biceps muscle laterally. 



N. glutjeus cranialis. — The cranial gluteal nerve is formed by branches 

 from the sixth and seventh lumbar nerves (possibly also from the first sacral). 

 It leaves the pelvis by the greater sciatic foramen, passes out between the 

 piriformis and deep gluteal muscles, runs between the deep and middle gluteals 

 supplying both, and ends in the tensor fasciae latse, mainly in the longer, oral 

 part of this muscle. 



N. glutjsus CAUdalis. — This rises from the seventh lumbar and the first 

 sacral nerves. It accompanies the sciatic nerve on the medial face of the 

 piriformis, where it divides into two branches to end in the superficial and 

 middle gluteal muscles. 



Aa. gltjt^ea cranialis et catjdalis. — Both the cranial and the caudal 

 gluteal arteries are branches of the parietal ramus of the hypogastric artery. 

 Leaving the parent vessel opposite the oral border of the piriformis muscle, the 

 cranial gluteal artery accompanies the nerve of the same name into the gluteal 

 mass of muscles. Very much larger, and virtually the terminal branch of 

 the parietal ramus of the hypogastric, the caudal gluteal artery accompanies 

 the sciatic nerve to the region of the hip-joint, and ends in the biceps and 

 Bemitendinosus muscles. 



M. obturator INTERNUS. — The origin of the internal obturator muscle 

 is within the pelvis, and, consequently, cannot be examined as yet. Its inser- 

 tion into the trochanteric fossa of the femur, however, should now be determined. 



Dissection. — Reflect the deep gluteal muscle, and so expose the origin of the 

 rectus femoris and capsularis muscles. 



