chap, xix.] HIP JOINT. 397 



and varies from one inch to half an inch in width. 

 The bone immediately above the articular area is 

 very dense, and through it is transmitted the superin- 

 cumbent weight of the trunk. The non-articular part 

 corresponds to the area enclosed by the horse-shoe, and 

 is made up of very thin bone. In spite of its thinness 

 it is very rarely fractured by any violence that may 

 drive the femur up against the pelvic bones, since no 

 ordinary force can bring . the head of the thigh-bone 

 in contact with this segment of the os innominatum. 



Pelvic abscesses sometimes make their way into 

 the hip joint through the non- articular part of the 

 acetabulum, and an abscess in the hip joint may reach 

 the pelvis by the same route. But both such circum- 

 stances are rare. In some cases of destructive hip 

 disease the acetabulum niay separate into its three 

 component parts. Up to the age of puberty these 

 three bones are separated by the Y-shaped cartilage. 

 At puberty the cartilage begins to ossify, and by .the 

 eighteenth year the acetabulum is one continuous mass 

 of bone. The breaking up of the acetabulum by disease, 

 therefore, is only possible before that year. 



The manner in which the various movements at 

 the hip are limited may be briefly expressed as follows. 

 Flexion, when the knee is bent, is limited by the con- 

 tact of the soft parts at the groin, and by some part 

 of the ischio-femoral ligament ; when the knee is ex- 

 tended the movement is limited by the hamstring 

 muscles. Extension is limited by the ilio-femoral or 

 Y ligament. Abduction by the pectineo-femoral 

 ligament. Adduction of the flexed limb is limited 

 by the ligameiitum teres and ischio-femoral ligament, 

 and of the extended limb by the outer fibres of the 

 ilio-femoral ligament and upper part of the capsule. 

 Rotation outwards is resisted by the ilio-femoral 

 ligament, and especially by its inner part, during 

 extension, and by the outer limb of that ligament and 



