382 THE GENITO-URINARY SYSTEM 



whereas the male pelvis represents a " long section of a short 

 cone." 



Congenital anomalies of the sacrum which influence the 

 size of the cavity or the apertures are not of frequent 

 occurrence. Occasionally the ala of the sacrum may fail to 

 develop, and this deficiency causes a marked diminution in 

 the oblique diameter of the pelvis (Ncegele pelvis). A still 

 rarer anomaly is the congenital absence of both alae (Roberts 1 

 pelvis). 



At the lumbo-sacral articulation the convexity of the lumbar 

 curve becomes continuous with the concavity of the sacral 

 curve at the sacral promontory (Fig. 134). In this situation 

 the vertebral column may be dislocated forwards on the 

 sacrum, as the result of an injury, the real significance of 

 which is often overlooked at the time of the accident owing to 

 the absence of nervous symptoms. As a result of this injury, 

 the antero-posterior diameter of the pelvic inlet is considerably 

 diminished, and the foetal head is prevented from entering the 

 pelvis (Spondylolisthetic pelvis). 



Other bony differences distinguish the female from the male 

 pelvis. The pubic crests are longer, and on this account the 

 acetabula have a more lateral inclination. The greater 

 trochanters, therefore, are more widely separated, giving the 

 subject an appearance of increased breadth. The medial 

 slope of the long axis of the femur is greater in the female, 

 and this difference constitutes a slight, but normal, degree of 

 knock-knee. 



The available space within the pelvic cavity is increased in 

 the female by the larger size of the pubic arch and of the 

 greater and lesser sciatic foramina. In addition, the spines 

 and tuberosities of the ischium, which tend to encroach on 

 the cavity in the male, are somewhat out-turned in the 

 female. 



The following tables, which are taken from Cunningham's 

 Text-Book of Anatomy, indicate the measurements of the 

 average female pelvis. 



