CHAPTER XXVIII. 



THE PELVIS. 

 THE BLADDER. SIGMOID FLEXURE 



Suprapubic Lithotomy. AND RECTUM. 



THE UTERUS, OVARY, ETC. Excision of Rectum. 

 Operations on 

 Structures felt per 

 Vaginam. 



The pelvis as a whole is formed by the ora innominata 

 and is divided into the true and the false pelvis. The 

 false is that portion which is bounded by the expanded 

 ilia, while the true forms a canal with an inlet, a body and 

 outlet. The line for the centre of gravity of the body, in 

 the upright position, passes down through the odontoid 

 process of the axis, then through the points of junction of 

 the curves of the vertebral column, to the sacro-vertebral 

 angle, thence downwards towards the front of the pelvic 

 cavity, so as to bisect a transverse line joining the heads of 

 the two femurs. The weight of the superimposed spinal 

 column is received upon the sacrum and tends to depress 

 that bone, so that its upper end would be forced down- 

 wards and forwards, and its lower end backwards and up- 

 wards. This rotation backward of the lower end is pre- 

 vented, however, by the action of the gluteus maximus, 

 the coccygeus, the levator ani and by the resistance offered 

 by the sacro-sciatic ligaments, and the curve of the sac- 

 rum is probably the resultant of this downward pressure 

 of the spinal column being opposed by the structures men- 

 tioned above. Further, the pressure would separate the 

 innominate bones in front by pulling on the posterior 

 spines through the sacro-iliac ligaments, were it not for 

 the powerful ligaments uniting the bones together at the 

 symphysis. 



