22 



OBSTETRICAL ANATOMY. 



sometimes in the Carnivora or in cases of hydrocepiialus ; and also 

 because the less value of animal life leads the operator, when in diffi- 

 culties, 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 dif- 

 ferent animals, in order not only to fully understand the mechanism of 

 parturition, but also with regard to the indications they may furnish in 

 many cases of dystokia. 



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

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

 widest below ; and that in the Carnivora it is somewhat cylindrical. 

 This diffei'ence in outline is conformable with the shape of the foetal 

 thorax, which in the former is deeper than it is wide, particularly at 

 the period of birth. During parturition, the foetus of Herbivorous 

 animals is so placed, generally, that the withers and shoulders are 

 towards the roof or superior plane of the pelvis ; while the sternum and 



iucee^ ^¥%«^ 



Fig. 15. Fig. 16. 



Median Section of the Pelvis of the Horse (Fig. 15) and Maee (Fig. 16). 



1, Sacrum ; 2, Two first Coccygeal Vertebra ; 3, Two last Lumbar Vertebrae ; 

 4, Ischio-pubic Sj-mphysis ; a h, Axis of the Pelvic Cavity ; c d, Supero- 

 inferior Diameter of the Inlet ; e f, Supero-inferior Diameter of the Outlet ; 

 c g, Vertical Diameter of the Inlet ; i h, Vertical Diameter of the ]Mid- 

 pelvis ; kf, Vertical Diameter of the Outlet. 



anterior limbs, which form a larger mass, rest on the floor or inferior 

 plane. The passage of the thorax of the foetus in these animals is, 

 apart from other causes, the chief difficulty in parturition. In the 

 human female, it is the head of the foetus. The thorax of the Carni- 

 vorous foetus is not nearly so deep, comparatively ; it is therefore better 

 adapted to pass through the nearly circular canal. 



The term diameter, in obstetrics, is emploj^ed to designate the distance 

 between certain points in the pelvic cavity, and by which, practically, 

 we may compare the capacity of that space with the volume of the 

 largest part of the foetus that has to pass through it. 



In the human species four diameters are usually given for the inlet 

 and outlet of the pelvis, and some veterinarians also furnish these 

 measurements. They are : (1) a vertical or sacro-pubic, from the sacro- 

 lumbar articulation to the ischio-pubic symphysis ; (2) a transverse, 

 passing between the most concave portion of the ilia ; and (3, 4) two 

 oblique, from the ilio-pectineal line of one side to the sacro-lumbar 

 articulation of the other. 



