POSTERIOR PART OF LOWER EXTREMITY. 375 



Greater Trochanter (Figs. 227 and 228). Muscles inserted into: (i) The 

 glutens inedins into the oblique line. (2) The glutens minimus into the anterior 

 surface. (3) The obturator externus into the digital fossa. (4) Into the superior 

 border, in the following order, from before backward : the pyrifonnis, the gcuuihis 

 superior, the obturator interims, and the gcmellus inferior. This is the logical 

 order of insertion, since they leave the pelvis in this order. (5) Into the base 

 you will see the vastus externus. (Fig. 228.) Now turn to figures 227 and 

 228 and study these insertions on the bone. In your dissection trace each 

 tendon to its complete insertion. 



Gluteus Maximus Insertion. This muscle is inserted into the gluteal 

 ridge of the femur. This is called the third trochanter when it is very large. 

 It is one of the constituent parts of the linea aspera. Turn to figure 227, and 

 study the linca aspera. (Read page 329 on linea aspera.) 



External Rotators of the Thigh. From the nature of the origin and in- 

 sertion of the pyriformis, gemelli, obturators, and quadratus femoris, they will 

 produce external rotation of the limb, when this is straight that is, when its 

 long axis parallels the long axis of the trunk, as in* the standing or recumbent 

 posture. In the sitting posture, however, when the limb is at right angles to the 

 trunk, they make 'traction parallel to the long axis of the femur, and thereby 



PATELLA 



Synovial membrane 



Capsule - 



FEMUR 



Crucial ligaments ! 



Vt^iHBfitoffiiS! SSMP.W Inner head of gastroccemius 



Biceps ^liisSFQm^SF^r"' Sartorius 



Outer head of gastroonemius - :S ^ ; C!>^ 5&ffiP^<?- Gracilis 



Popliteal artery 



EXTERNAL POPLITEAL NERVE ^^ ^" *^ ^Sem.-membranosus 



Popliteal rein ' 

 INTERNAL POPLITEAL NERVE / Semi-tendinosua 



External saphena vein 



FIG. 261. HORIZONTAL SECTION OF THE KNEE-JOINT. (One-half.) 



become physiological abductors and antagonize the adductor group. The obtura- 

 tor externus remains an external rotator even in the sitting position. Pull the 

 cadaver to the edge of the table, and make this simple demonstration at this 

 stage of your dissection. 



Demonstrate on yourselves external rotation (i) in the standing position ; 

 (2) in the sitting position. In the first case notice the ease with which you may 

 turn the whole limb outward. This act was done with ease because the six 

 external rotators participated in the act. It would be very much more difficult 

 to do if five of these refused to act. This is exactly what occurs when you sit 

 and do external rotation, since five of these muscles cease to be external rotators 

 when exerting traction in the long axis of the limb, as they do in the sitting 

 posture. In the standing position six muscles are exerting traction in the 

 region of the greater trochanter almost at right angles to the long axis of the 

 femur. This makes external rotation easy. In sitting, only one muscle is left 

 to do this work /. e., the external obturator muscle. 



Internal Rotators of the Thigh. The anterior segments of the glutens 

 mcdins and miniums rotate the thigh inward. 



Tendon of Obturator Internus. To show this tendon, carefully separate the 



