THE HIP-JOINT. 243 



.The ligamentum teres is attached by its apex into a 

 fossa just behind and below the centre of the globular 

 head of the bone, and by its base to the margins of the 

 notch at the bottom of the acetabulum, and its office is 

 to check external rotation and adduction when the thigh 

 is flexed, thus assisting in the prevention of dislocation 

 of the head forwards and outwards. The bottom of the 

 cotyloid cavity is very thin, and is liable to perforation 

 in caries, in which case the pus invades the pelvic cavity. 

 It may be opened by the point of the knife in amputa- 

 tion through the hip-joint, or in the subsequent gouging 

 after resection, unless care be taken. It is a somewhat 

 remarkable fact that after the operation of disarticula- 

 tion, or in the case of old unreduced dislocation, the 

 cavity contracts. 



The vessels which supply the articulation are the obtur- 

 ator, ischiatic, internal circumflex, and gluteal ; and the 

 nerves are from the great sciatic, obturator, and accessory 

 obturator, and they enter it either by means of the notch, 

 or through the ligamentum teres. 



Dislocation of the Head of the Femur. With regard to 

 the displacements of the head of the femur in dislocation, 

 none of the muscles of the gluteal region probably exert 

 any influence excepting the obturator interims, the mus- 

 cular substance of which is so mixed with tendinous 

 structure as to give it great strength ; and when in a 

 state of contraction it may be regarded as an accessory 

 ligament to the joint. 



The regular dislocations of the head of the thigh bone 

 are (1) upwards, on to the dorsum ilii ; (2) backwards, 

 into the great sciatic arch ; (3) downwards, into the ob- 

 turator foramen, and (4) forwards, on to the pubes. In 

 the first form the limb is shortened from one to two and 



