374 



HUMAN ANATOMY. 



resistance of the strong ilio-femoral ligament, excepting the outer band. Abduction 

 is Hmited, the thigh being extended, by the pubo-femoral Hgament and perhaps by 



the inner Hmb of the iho-femoral. 



Fig. 390 



Round ligament 



Capsule 



When the thigh is flexed, the latter is 

 certainly relaxed, and the strain comes 

 on the pubo-femoral and a part of the 

 capsule behind it, — a very weak re- 

 gion. Adduction with a straight thigh 

 is limited by the outer limb of the 

 ilio-femoral, the top of the capsule, 

 and Morris's band from the rectus 

 tendon to the vastus externus, if it 

 be present. After moderate flexion 

 is passed, the ilio-femoral is relaxed. 

 Outward rotatioii, the thigh being 

 straight, is checked by the ilio-femoral, 

 especially by its inner band. As the 

 thigh is flexed the inner band is re- 

 laxed and the outer is at first tense, 

 but both are relaxed as flexion reaches 

 about 45°. Morris's band now be- 

 comes tense, and as flexion becomes 

 extreme the round ligament is tense 

 also, unless the thigh be abducted, 

 when it is completely relaxed. In- 

 ward rotation is checked by the ischio- 

 femoral ligament in any position. 



The most important part of the 

 capsule is the ilio-femoral band, which 

 is extremely strong and prevents over- 

 extension. It is an essential element 

 in maintaining the upright position. 

 The round ligament has probably no 

 mechanical function, though it can be 

 made tense by flexing, and at the same 

 time either adducting the femur or 

 rotating it outward. It is too weak to be of any real use as a restraint. Probably 

 its chief usefulness is to carry vessels to the head of the femur in childhood. 



Retinaculum 



Posterior 



intertrochanteric 



ridge 



Lesser 

 trochanter 



Right femur seen from inner side, showing reflection of 

 synovial membrane onto the neck. 



PRACTICAL CONSIDERATIONS. 



The greater security of the hip-joint, as compared with the shoulder-joint, is 

 due to the depth of the acetabular cavity ; to its reinforcement by the cotyloid fibro- 

 cartilage ; to the attachments of the ilio-psoas, gluteus minimus, and vastus externus 

 to the capsule ; but chiefly to the thickenings of the capsule itself, which are described 

 as the ilio-, ischio-, and pubo-femoral ligaments. 



The greatest pressure upon the capsule in all ordinary positions is in an upward 

 and outward direction, or upon the anterior surface of the capsule, as when, under 

 the influence of the powerful extensors, the pelvis and trunk tend to roll backward 

 upon the thighs in the erect posture. The tension and pressure are, of course, 

 greatest near the pelvic attachment of the capsule where the head will impinge upon 

 it with the most advantage as to leverage. The capsule is especially fitted to resist 

 this pressure. 



If two lines be drawn, one from the anterior inferior iliac spine to the inner 

 border of the femur near the lesser trochanter, the other from the anterior part of 

 the groove for the external obturator {i.e., the upper part of the tuberosity of the 

 ischium) to the digital fossa, all the ligament outside and above these lines is very 

 thick and strong ; whereas, all to the inner side and below, except along the narrow 

 pubo-femoral band, is very thin and weak, so that the head of the bone can be 



