26 OBHTETRICAL ANJT03IY. 



attention to pelvimetry in animals, points out the means whereby the 

 diameters of the inlet may be attained. ^ 



This method is, however, so complicated and unsatisfactory, that it 

 requires further elaboration before it can be recognised as useful and 

 reliable. 



Saint-Cyr has endeavoured, in a somewhat similar manner, to arrive 

 at some criterion as to the diameters of the inlet of the pelvis — which 

 is, after all, the most important in parturition — in the living animal 

 For the sacro-jmhic diameter, he has taken for guide the height of the 

 Mare, supposing that the two should be nearly always constant in their 

 relations ; and to fix this relation, the diameter was measured in twenty- 

 eight animals of various sizes. Taking the average of these twenty-eight 

 measurements, and dividing it by the average of the heights, the quotient 

 obtained gave the co-efficient, by which it was necessary to multiply the 

 height of any Mare to find the sacro-pubic diameter of its pelvis. For 

 the transverse or bis-iliac diameter, the width of the croup measured 

 between the external angles of the ilia (taken by a tape), or between the 

 coxo- femoral articulations (taken by a large pair of compasses), was 

 adopted. But it was soon discovered that one and the same co-efficient 

 would not serve for all cases ; as in common-bred lymphatic horses, the 

 bones are large, the soft textures abundant, and the pelvic cavity less 

 than would be surmised from the width of the croup ; while in those 

 which are well-bred, the bones are smaller and denser, the soft tissues 

 more condensed, and the pelvic space large, comparatively speaking. 

 So that the co-efficient had to be less in the latter than the former. 



The results of Saint-Cyr's measurements and calculations are fairly 

 reliable, and the external measurements do not differ very widely in 

 their indications from those furnished by actual measurement of the 

 pelvic cavity. 



This method, however, even when accepted as perfectly reliable, only 

 furnishes us with the dimensions of the well-formed normal pelvis ; it 

 gives no information with regard to internal deformities, for the estima- 

 tion of which it is necessary to have recourse to ' direct exploration,' 

 either through the vagina or rectum, by which we may not only dis- 

 cover the character, but also, approximately, the extent of the deformity. 

 "Internal pelvimetry" may also be resorted to in this way; and in 

 practice, after a little experience, it will be found sufficiently simple and 

 trustworthy to be of much service. This internal measurement of the 

 pelvic cavity cannot be satisfactorily made by means of compasses or 

 other instruments in the living animal, as in w^oman ; but the hand may 

 be successfully employed in ascertaining the different diameters by 

 spans — as the thumb from the index to the middle finger, and even 

 widely spread to the little finger ; the distance between these being pre- 

 viously known, we may readily ascertain with sufficient accuracy the 

 diametrical capacity of the pelvis. 



The axis of the jjelvis is the term given to an imaginary line drawn 

 through the pelvic canal from before to behind, at an equal distance 

 from the circumference. In the human pelvis there are ttoo axes — 

 those of the upper and lower outlet, and a knowledge of them is of 

 much importance in midwifery ; they form an obtuse angle with each 

 other, and, when combined with the inclination of the pelvis, w^e observe 

 that the direction the human foetus must take is somewhat tortuous or 



1 The calculations and measurements are given in Saint-Cyr's " Traite d'Obstetrique 

 Veterinaire," second edition, p. 26. 



