24 OBSTETRICAL ANATOMY. 



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

 requires further elaboration before it can be recognized as useful and 

 reliable. 



Saint-Cyr has endeavored, 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-piibic diameter, he has taken for guide the height of the Mare, 

 supposing that the two should be nearly always constant in their rela- 

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

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

 urements, and dividing it by the average of the heights, the quotient ob- 

 tained 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, t\\Q vj'idxh. oi the croup measured between 

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

 moral 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 discover 

 the character, but also, approximately, the extent of the deformity. " In- 

 ternal pelvimetry " may also be resorted to in this way ; and in practice, 

 after a little experience, it will be found sufficiently simple and trust- . 

 worthy to be of much service. This internal measurement of the pelvic 

 cavity cannot be satisfactorily made by means of compasses or other in- 

 struments in the living animal, as in woman ; but the hand may be suc- 

 cessfully 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 previously known, 

 we may readily ascertain with sufficient accuracy the diametrical capacity 

 of the pelvis. 



ThQ axis of the pelvis IS the term given to an imaginary line drawn 

 through the canal of the region from before to behind, at an equal dis- 

 tance from the circumference. In the human pelvis there are two axes — 

 those of the upper and lower oudet, 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, we observe that 

 the direction the human foetus must take is somewhat tortuous or curved. 

 In animals there is only one axis, and that is almost rectilinear : the 

 sacro-vertebral angle or "promontory" being comparatively little de- 

 veloped, and the sacrum passing almost in a direct line from the vertebral 



