THE HIND EXTREMITY. 267 



is accompanied by two roots of vena profunda femoris, and 

 a branch of arteria profunda femoris. Inferiorlj it breaks 

 up to form the anterior and iiosterior tibial, and popliteal 

 nerves. In its course down the limb it gives off fibres to 

 all the large muscles among which it runs. Bj removal of 

 the above-mentioned structures we are enabled to see 



Ischio-femoralis, which arises from the under surface of 

 the neck of the ischium, and becomes inserted with the ten- 

 dinous band of triceps abductor femoris to the posterior 

 surface of the femur midway between the two small tro- 

 chanters ; it is triangular and fleshy ; also the four 

 muscles which become inserted into the fossa behind 

 trochanter major are thus exposed ; these are 



Obturator externus, which arises from the under surface 

 of the obturator ligament and the margins of the obturator 

 foramen. It resembles a number of small muscles united 

 together. 



Gemini vel iscMo-trochanterius, composed of two very 

 similar united portions, which arise from the under surface 

 of the neck of the ischium in front of ischio-femoralis. 



Obturator internus, which arises within the pelvis from 

 the upper surface of the obturator ligament, is superiorly 

 covered by a reflection inwards of the sacro-sciatic liga- 

 ment and is also attached to the margins of the obturator 

 foramen. This muscle combines with 



Pyriformis, arising from the posterior part of the venter 

 ilii, as high up as the transverse process of the first sacral 

 vertebra. The tendon common to the two gains exit from 

 the pelvis by passing between the sacro-sciatic ligament 

 and the neck of the ischium in winding round the bone, 

 where it is lubricated by synovia; it then blends with 

 obturator externus and gemini in passing to their common 

 insertion. The limb may now be removed from the trunk 

 by sawing through the middle of the femur transversely. 

 The gastrocnemii muscles may then be examined. 

 _ Gastrocnemius externus arises by two heads from the 

 ridges bounding the fossa on the postero-inferior part of 

 the femur inclined to the outer side, one from the inferior 

 third of the external surface, the other from the inferior 

 third of the posterior surface of that bone. The external 

 head is covered by a hroad aponeurotic hand, which runs 

 to form a sheath for gastrocnemius externus, after receiving 

 a band from the aponeurosis of gracilis. It then meets a 



