DISSECTION OF THE DOG 83 



caudal gluteal vessels, the posterior cutaneous femoral nerve runs parallel to the 

 sacro- tuberous ligament as far as the border of the superficial gluteal muscle. 

 Here it becomes superficial, and passes along the groove between the biceps and 

 semitendinosus muscles to supply the skin over the back of the thigh. Large 

 perineal branches (rami perineales) supply the region of the anus. 



M. glutjeus medius. — The middle gluteal muscle is strong and thick, 

 and occupies the depressed lateral surface of the ilium. Its origin is from 

 the iliac crest and the fossa on the lateral surface of the ilium. Some fibres 

 also arise from the tendon of origin of the shorter belly of the tensor fasciae 

 latse. The muscle is inserted into the trochanter major of the femur. 



Dissection. — Reflect the biceps muscle about the middle of its length. 

 In doing so, observe a thin, narrow band of muscle crossing its deep face 

 somewhat obliquely. This is the m. abductor cruris posterior, which takes 

 origin, by means of a feeble tendon, from the sacro-tuberous ligament. 

 The distal part of this little muscle forms the apparent caudal border of 

 the biceps, with which the abductor finally blends. 



Observe lymph-glands (lympho-glandulse poplitese) lying on the gastro- 

 cnemius between the abductor cruris posterior and the semitendinosus 

 muscles. 



Under the biceps there is a strong intermuscular septum attached on the 

 one hand to the linea aspera of the femur, and continuous on the other 

 with the fascia lata of the thigh. This will require to be reflected so 

 that the lateral vastus muscle may be clearly demonstrated. 



In order to adequately expose the deep gluteal structures it is necessary to 

 remove the greater part of the middle gluteal muscle. This must be 

 done with great care. 



M. glutjeus PROFUNDUS. — The deep gluteal muscle lies close upon the hip- 

 joint. Its fibres arise from the sciatic spine and the adjacent part of the 

 lateral surface of the ilium. The insertion of the muscle is into the trochanter 

 major of the femur. 



M. piriformis. — This muscle is immediately behind the deep gluteal. 

 Taking origin from the lateral border and the ventral surface of the sacrum, 

 its insertion is into the trochanter major close to, or blended with the 

 insertion of the middle gluteal muscle. 



Mm. gemelli. — Though named in the plural there is really only one muscle 

 the origin of which is from the lateral surface of the ischium, and the insertion 

 into the trochanteric fossa of the femur. 



M. vastus lateralis. — The lateral vastus muscle is the most powerful 

 member of the quadriceps group. It arises mainly from the anterior surface 

 of the femur immediately distal to the greater trochanter. A small pro- 

 portion of the muscle also arises from the lateral Up of the linea aspera. Joining 



g 2 



