20 



OBSTETRICAL ANATOMY 



is nearly cylindrical. The ischium^ immediately above the obturator fora- 

 men, rises abruptly to almost a right angle ; this is the narrowest part of 

 the canal, and here it is that the passage of the foetus is obstructed in 

 small females which have been impregnated by large dogs. It must be 

 remarked, however, that the late, and often incomplete, ossification of 

 the symphysis allows a certain amount of dilatation of the canal, and 

 renders the passage of a comparatively large foetus possible. 



SECTION IV. CAPACITY OF THE PELVIS OR PELVIMETRY. 



We have already casually alluded to the capacity of the pelvic cavity in 

 the larger domesticated animals, and to its diameters ; and it will be in- 

 ferred that these must vary with the different sizes existing in the Mare, 

 Cow, Pig, and Bitch, though in others which are generally of uniform 

 volume — as the Sheep, Goat, Ass, ayd Cat — the pelvis does not offer 

 much diversity. In this respect the latter species resemble mankind, in 

 the female of which a difference in size does not make much difference 

 in pelvic dimensions : half an inch probably covering the variations. But 

 in the Mare or Cow, if we compare a small with a large animal, this dif- 

 ference in diameters may extend to nearly two or three inches. 



The subject oi pelvimetry is very important to tlie accoucheur of the hu- 

 man species, as the female pelvis is particularly liable to be deformed or 

 defective in its proportions. It is not nearly of so much moment to the 

 veterinary obstetrist, as the head of young animals generally experiences 

 no difficulty in passing through the pelvic cavity, except sometimes in the 



Fig. 8. Fig. 9. 



Medium Section of the Pelvis of the Horse (Fig. 8) and Mare (Fig. 9). 



I, Sacrum ; 2, Two first Coccygeal Vertebrae ; 3, Two last Lumbar Vertebrae ; 4, Ischio-pubic 

 Symphysis: a, b, Axis of tlie Pelvic Cavity; c, d, Supero-inferior Diameter of the Inlet; 

 e, /, Supero-inferior Diameter of the Outlet ; c, g. Vertical Diameter of the Inlet ; i, h, 

 V&rtical Diameter of the Mid-pelvis ; k,/, Vertical Diameter of the Outlet. 



carnivora or in cases of hydrocephalus ; and also because the less value 

 of animal life leads the operator, when in difficulties, to sacrifice the foetus 

 rather than endanger the existence or value of the mother. 



It is, nevertheless, useful to know the diameters of the pelvis of differ- 

 ent animals, in order not only to fully understand the mechanism of par- 

 turition, but also with regard to the indications it may furnish in many 

 cases of dystokia. 



We have shown that the pelvic canal in the large and small herbivors 

 is sojiriewhat of an oval shape, the narrowest part being above, and the 



