THE PELVIS. 



105 



interval between the sacrum and coccyx and the ischium on each side 

 is bridged over in the recent state by the sacro-sciatic ligaments, which 

 therefore assist in bounding the outlet of the pelvis. 



Position of the Pelvis. — In the erect attitude of the body, the 

 pelvis is so inclined that the plane of the brim of the true pelvis forms 

 an an^le with the horizontal, which varies in different individuals from 



Fit:. 92. 



Figs. 92 & 93. 



Sketches of the Male 

 AND Female Pelvis 



AS seen from above 

 AND IN FRONT. (A. T. ) 



In fig. 90 of clie fe- 

 male pelvis the lines are 

 shown in which the ili- 

 mensions of the iielvis 

 are usually measured at 

 the brim. 



a, p, antero-posterior 

 or conjugate diameter ; 

 t, r, transverse or 

 widest diameter ; o, b, 

 0, b, oblique diameters. 



In the original speci- 

 mens, which were se- 

 lected as giving the full 

 average dimensions, the 

 following were the mea- 

 surements in inches : — 



Antero-posterior dia- 

 meter — female, 4i ; 

 male, 4. Transverse 

 diameter— female 5\ ; 

 male, 4.^. Oblique dia- 

 meter — female, 5 ; male, 



60°toC5°. Thebase 

 of the sacrum was 

 found by Niigele 

 in a large nuiiil;er 

 of well-formed female bodies to be about ;3| inches above the upiier 

 margin of the symphysis pubis; the level of the top of the coccyx 

 lie found varying from 22 lines above the apex of the pubic arch 

 to 9 lines below the same point, and on an average to be 7 or 8 

 lines above it (Niigele, "Das weibliche Becken," &c., Carlsruhe, 1825 ; 

 "Wood, article " Pelvis " in the Cyclopedia of Anatomy and Physiology). 

 The pelvic aspect of the sacrum, near its base, looks much more down- 

 wards than forwards, hence the sacrum appears at first sight to occupy 

 the position of the keystone of an arch ; but being in reality broader at 

 its pelvic than on its dorsal aspect, it is a keystone inverted, or having 

 its broad end lowest, and is supported in its place chiefly bycartilage 

 and ligaments, but also to a slight extent by the inward projection of 

 the anterior margin of the iliac articular surface. The line of pressure 

 of the weight of the body on the sacrum is directed downwards towards 

 the symphysis pubis, aiid the resistance of the head of the thighbone 

 on each side is directed upwards and inwards. 



