DYSTOKIA FIKHI fELl'IC CONSTRICTION. 291 



two diameters. The dia^'nosis may not be so easy, however, when the 

 canal is partly or wholly occupied by the fcetus. 



Another kind of deformity described by several authorities, consists 

 in a depression of the sacrum (lordosis), which is recognised externally 

 by an abrupt hollow existing towards the posterior third of the croup. 

 By rectal exploration the sacrum is found to constitute a projection 

 in the roof of the pelvis, at the lower face of the bone, and this 

 diminishes the supero-inferior diameter of the cavity to an extent 

 corresponding to the protuberance. 



Exostoses. 



Exostoses on the pelvic bones, and particularly when they project 

 into the pelvic cavity or encroach on its openings, may become a 

 more or less serious obstacle to the passage of the fuetus (Fig. 82). 



ffe= 



.^ 



Pelvic Exostosls. 



Favre, of Geneva, states that bony tumours situated beneath the 

 croup, at the inner and upper surface of the pelvis, render parturition 

 ditBcult, even if they are not large and near the root of the tail. lie 

 atlds that such cases are not rare in old Mares. 



Fractures. 



Like the exostoses, more or less completely consolidated fractures 

 of the sacrum or coxa;, which have been united by an irregular callus, 

 may, for the same reason, prove an obstacle to birth. As animals 

 suffering from a fracture of any of the bones of this region are often 

 destroyed, laborious parturition from such a deformity is not so frequent 

 as from some other causes ; nevertheless, it does occur now and again. 



It must be remembered that fractures of the pelvic bones are some- 

 what frequent in animals, and may occur at any part. The most 

 common seat of fracture is perhaps the external angle of the ilium ; 



