182 



TEE BONES. 



pubis ; and on the sides by a part of the inner face of the iliac bones, and also 

 the internal aspect of the pectineal crests. 



The inlet presents four diameters, a knowledge of which is important in 

 obstetrics — a vertical, horizontal, and two oblique. The first, the sacro-pubir, 

 extends from the inferior face of the sacriun to the anterior border of the pubic 

 symphysis ; its mean length is 8:^ inches. The second, the bis-iliac, is measured 

 from one pectineal crest or eminence to another ; the mean of this is H^jj inches. 

 The two last diameters, the ileo-sacral, are estimated from the inferior face of 

 the sacro-iliac articulation of one side to the ilio-pectineal eminence of the 

 other ; this is, on an average, SyV inches. These measurements irrefutably 



Fig. 86. 



PELVIS OF THE HORSE. 



demonstrate that the inlet is not elliptical in the vertical direction ; but it may 

 happen that the transverse diameter is the greatest. 



The posterior aperture or outlet, situated at the posterior end of the pelvic 

 cavity, gives exit to the rectum and genital organs. It is limited by the inferior 

 face of the summit of the sacrum, the superior face of the ischial bones, the 

 supra-cotyloid crest or ischiatic spine, and the internal face of the sacro-sciatic 

 ligaments. At the outlet only two diameters are recognized — a vertical and a 

 horizontal. The vertical, extending from the inferior face of the sacrum to the 

 superior face of the ischial symphysis, measures on an average 6yV inches. 

 The horizontal diameter, comprised between the two supra-cotyloid crests, is 

 7-j^ inches. 



The superior face of the pelvic cavity is a little concave from before to 



