150 



ARTICULATIONS OF THE PELVIS. 



syrcphysis. The superior and posterior ligaments consist of only a few fibres 

 on the upper and back part of the articulation. The inferior or subpubic liga- 

 ment, thick and triangular, is attached to the rami of the pubic bones, gives 



Fig. 138. 



Fig. 138. RIGHT HALF OP A FEMALE 

 PELVIS, SEEN FROM THE INNER SIDE. 

 AN OPENING HAS BEEN MADE INTO 

 THE ACETABULUM TO SHOW THE 

 TIGHTENED CONDITION OF THE ROUND 

 LIGAMENT WITH THE FEMUR PAR- 

 TIALLY FLEXED AND ADDUCTED. f 



1, supraspinous ligaments descend- 

 ing to the sacrum from 2, 2, the 

 lumbar spinous processes ; 3, 4, the 

 lumbar and sacral spinal canal, with 

 its periosteal lining ; 5, placed on 

 the ilium above the anterior sacro- 

 iliac ligament ; 6, placed in the great 

 sacro- sciatic foramen, points to the 

 lesser sacro-sciatic ligament ; 7, greater 

 sacro-sciatic ligament, with 7', its 

 continuation over the inner border of 

 the tuberosity of the ischium ; 8, a 

 portion of the wall of the cotyloid 

 cavity, removed so as to give a view 

 from the inside of the head of the 

 femur, 9, with the round ligament 

 put upon the stretch, the femur 

 being partially flexed and ad ducted ; 

 10, the inner pait of the capsular 

 ligament relaxed ; 11, the shaft of 

 the femur. 



smoothness and roundness to the upper part of the subpubic arch, and 

 forms part of the outlet of the pelvis. 



The obturator membrane or ligament is a fibrous septum attached to the 

 border of the thyroid foramen, which it closes in its entire extent, except at 

 the upper and outer part of its circumference, where a small oval canal is 

 left for the obturator vessels and nerve. The membrane is fixed accurately 

 to the bony margin at the upper and outer sides of the foramen, and to the 

 posterior surface at the inner side. The obturator muscles are attached to 

 its surfaces. 



MOVEMENTS. In ordinary circumstances there is very little movement allowed 

 between the bones of the pelvis. In the erect posture the sacrum is thrown so 

 much backwards, that none of the advantage of the key-stone of an arch is ob- 

 tained by the tapering of its form from base to apex. It is only by the sinuosities 

 of its auricular surfaces that it directly presses on the hip-bones ; and as the width of 

 the bene rather diminishes at the upper or ligamentous part, the principal strain 

 is borne by the posterior sacro-iliac ligaments, from which the sacrum is in great 

 measure suspended (see fig. 139) as is well illustrated by the giving way and 

 bending inwards and downwards of their iliac points of attachment in rickety 

 deformities of the pelvis. Thus the structure of the sacro-iliac articulation gives 

 elasticity. The small amount of movement which is allowed between the bones of the 

 pelvis in the ordinary state is increased during parturition in this way, that the lower 

 part of the sacrum being pressed backwards, the wider part of the edge formed by 

 this bone is forced farther between the ossa innominata, so as to separate them to a 

 greater degree, and thus to increase the capacity of the pelvis. In some subjects it 

 would appear that in pregnant women a slight amount of separation may occasionally 

 occur at the symphysis from the extreme looseness of the connecting parts ; but in 

 general it is more probable that the only motion at the symphysis is the hinge-like 

 movement of the ossa innominata just described, and that the cavity of the pelvis 



