6 Veterinary Obstetrics 



wards from their sacral articulation, their inner borders being 

 concave. They attain their greatest distance from each other 

 soon after leaving the sacrum, near the great sciatic notch, at 

 the point where the flattened anterior portion merges into the 

 shaft, from whence they converge slightly as they approach the 

 cotyloid cavities. The ilia form the major portion of the lateral 

 walls of the pelvic inlet. 



The ischium is an irregular triangular, flattened bone, consti- 

 tuting the most posterior portion of the pelvis and concurring 

 with the pubis in the formation of the pelvic floor. It occupies 

 an almost horizontal position in the horse and most domestic ani- 

 mals, but, in the cow, its posterior portion is directed upwards and 

 backwards and compels the fetus, during its expulsion, to pass 

 obliquely upwards and backwards, instead of horizontally back- 

 wards. Anteriorly, it constitutes internally the posterior bound- 

 ary of the foramen ovale and, externall5% concurs in the formation 

 of the acetabulum, where it articulates with the ilium and pubis ; 

 on the median line it unites throughout its anterior part with the 

 corresponding bone of the opposite side, constituting the pos- 

 terior portion of the pelvic symphysis. 



The postero-external angles of the ischia are tuberous, consti- 

 tuting the ischial tubero.sities and between these is the receding 

 angle known as the ischiatic notch, which depends largely upon 

 the extent of the tuberosities for its depth while its width is fixed 

 by the degree of divergence of the two bones. 



This triangular notch varies greatly with species and individ- 

 uals and some authors contend that it is wider and more ample 

 in the mare than in the horse. The latter contention is not well 

 established and, if it exists, is not sufficiently marked to consti- 

 tute a means for differentiation between the sexes. 



The ischium is of little obstetric significance in domestic ani- 

 mals, except possibly in the cow, where the notch may be very 

 deep and narrow and the tuberosities, being very prominent and 

 directed sharply upward toward the coccyx, tend to limit the di- 

 mensions of the pelvic outlet and constitute a barrier to the pas- 

 sage of the fetus. 



The pubis is a flattened bone placed transversely at the anter- 

 ior border of the pelvis, articulating ou the median line with the 

 corresponding bone of the opposite side to constitute the floor of 

 the pelvic inlet. It articulates posteriorly with the ischium and 



