.592 DISSECTION OF THE THIGH. 



in stooping, instead of extending it and raising the trunk like the other 

 external rotator muscles. 



THE SACRO-SCIATIC LIGAMENTS pass from the innominate bone to the 

 sacrum and the coccyx ; they are two in number, and are named large 

 and small. 



The large or posterior ligament (fig. 201, p ) is attached internally to the 

 posterior part of the hip bone, and to the side of the sacrum and coccyx ; 

 and externally it is inserted into an impression on the inner and anterior 

 part of the ischial tuberosity, sending upwards a prolongation along the 

 pubic arch. It is wide next the sacrum, but is contracted towards the 

 middle, and is expanded again at the tuberosity. On the cutaneous sur- 

 face are the branches of the sacral nerves ; and the glutens maximus con- 

 ceals and takes origin from it. Branches of the gluteal and sciatic arteries 

 perforate it. 



The small ligament will be seen on dividing the other near the hip bone. 

 At the sacrum and coccyx it is united with the large band, but at the 

 opposite end it is inserted into the ischial spine. It is less strong than the 

 superficial ligament, by which it is concealed ; and it rests on the coccy- 

 geus muscle. 



By their attachments these ligaments convert the large sacro-sciatic 

 notch of the dried pelvis into two apertures or foramina. Between their 

 insertion into the spine and tuberosity of the innominate bone, is the small 

 sacro-sciatic foramen, which contains the internal obturator muscle with 

 its nerve and vessels, and the pudic vessels and nerve. And above the 

 smaller ligament is the large sacro-sciatic foramen, which gives passage to 

 the pyriformis muscle, with the gluteal vessels and the superior gluteal 

 nerve above it, and the sciatic and pudic vessels and the sacral .plexus 

 below it. 



SECTION III. 



THE BACK OF THE THIGH. 



Directions. The ham or the popliteal space may be taken after the 

 buttock, in order that it may be seen in a less disturbed state than if it 

 was dissected after the examination of the muscles at the back of the thigh. 

 When this space has been learnt the student will return to the dissection 

 of the thigh. 



Position. The limb is to remain in the same position as in the dissec- 

 tion of the buttock. 



Dissection (fig. 202). To remove the skin from the popliteal region let 

 an incision be made behind the knee for the distance of six inches above, 

 and four inches below the joint. At each extremity of the longitudinal 

 cut make a transverse incision, and raise the skin in two flaps, the one 

 being turned outwards and the other inwards. 



In the fat are some small cutaneous nerves and vessels, viz., one or two 

 twigs in the middle line of the limb from the small sciatic nerve and 

 artery beneath the fascia ; and some offsets of the internal cutaneous 

 nerve towards the inner part. After the subcutaneous fat is removed, 

 the special fascia of the limb will be brought into view. 



