1. A high incidence of paraplegia following operations for the correction of severe scoliosis in adults led to an investigation of the normal blood supply of the human spinal cord.

2. This entailed three methods of study: micro-dissection of the vessels of the spinal cord in thirty-five cadavers; radiological measurements of the spinal canal in fifty healthy subjects; and a study of the macerated spinal column in six adult cadavers.

3. The blood supply of the spinal cord is shown to be least rich, and the spinal canal narrowest, from the T.4 to approximately the T.9 vertebral level. This is named the critical vascular zone of the spinal cord, the zone in which interference with the circulation is most likely to result in paraplegia.

1. Two cases of recurrent post-traumatic dislocation of the hip are reported.

2. The literature is reviewed and the rarity of the condition is emphasised. Only twenty-two cases have been previously reported, eleven in adults and eleven in children.

3. The sequence of events leading to recurrent dislocation is not understood but the following important facts emerge. The initial incident could not be distinguished from that causing uncomplicated dislocations. There was a significant delay in reduction in a number of cases. Subsequent dislocations followed minor injury. A large defect in the posterior capsule with a large synovial-lined pouch or false joint was found at operation in both our cases. The ligamentum teres was not seen at operation. The surgeon was unable to redislocate the hips during the operation.

4. In both cases reported here treatment was by excision of the posterior pouch and repair of the capsular defect.

5. Based on the above facts some tentative deductions are made.

1. The strength of the pelvic arch depends on the integrity of the anterior interpubic ligament, whose strength has been demonstrated by dissections. Once that ligament is divided the sacro-iliac ligaments offer little resistance to opening out of the pelvis.

2. The structure of the pelvis and hips is compared to an arcade formed by a central and two lateral arches. The weight of the trunk is transmitted to the lower limbs through this arcade.

3. Fractures of the pelvis are classified according to the mechanism of production. The case for anatomical reposition and internal fixation is stated, and case histories are given to illustrate the disabilities due to persistent deformity.

4. Reduction can be achieved as late as two or three weeks after injury. However, if early operation for visceral injury is necessary, there is a strong case for combining this with open reduction and fixation. In some cases the patient's general condition may preclude such procedures, but more usually the additional manipulations cause little additional operative shock and are fully justified by the subsequent increased comfort of the patient and the greater ease of nursing.

This review shows that inter-body spinal fusion can be achieved in a satisfying percentage of cases, and the assertion that there is an intrinsic factor peculiar to the vertebral bodies which prevents such a fusion cannot be supported. The operation has a limited but definite place in the field of spinal surgery, and should be reserved for those patients with spinal instability associated with intractable and persistent backache. Spondylolisthesis is the indication par excellence. A new operative technique, which has been developed during ten years, has become standardised. The trans-sacral approach provides a better and safer exposure than those described before. In the event of failure of inter-body fusion, it is suggested that further attempts at grafting should be restricted to one of the posterior methods which have a 75 per cent chance of producing successful bony fusion.

Clinical photographs are reproduced in Figures 16 to 18 to show that patients suffering from a painful spondylolisthesis may be restored to normal activity by this operation.