54 BOVINE OBSTETKICS 



2. A knowledge of these dimensions allows us to under- 

 stand the mechanism of parturition better, and shows how the 

 foetus accommodates itself to the pelvic inlet. Discussion of 

 the mechanism of parturition later will show how the calf gets 

 through the inlet. Let it be mentioned here, that during 

 expulsion the head, resting upon the forelegs, lies in the 

 vagina, the sterno-dorsal diameter of the calf's thorax runs 

 parallel with the vertical line, starting from the symphysis, the 

 diameter of which is greater than the transverse diameter of 

 the inlet, which runs parallel with the smaller bicostal diameter 

 of the thorax. 



This, therefore, is favorable for the passage of the foetus, 

 although the dimensions become somewhat modified, as the 

 ribs are pushed back on the thorax and can be compressed 

 decidedly. 



3. The practice of pelvimetry becomes necessary when 

 during pregnancy stenosis is present, be it the result of 

 fractures, formation of exostoses or dislocation of the sacrum. 



During gestation, disturbances may be present or arise, 

 inducing changes in pelvic dimensions. Fracture of the 

 external angle of the ilium, quite common, does not produce 

 pelvic stenosis ; but fracture of the internal ilial angle or shaft 

 of the ilium may do so ; the dislocation, as well as the callus 

 following it, may diminish the transverse diameter of the inlet. 

 Fractures of the pubis and ischium may also lessen the pelvic 

 diameters by callus formation. 



Descent of the sacrum resulting from rupture of the 

 ligamentous apparatus between it and the ilium, may materi- 

 ally decrease the height of the pelvic inlet. This dislocation 

 is not accompanied by a disturbance in the union of the 

 sacrum and last lumbar vertebra, but the most posterior 

 portion of the vertebral column is lowered. The internal iliac 

 angle projects, and one feels the tensely stretched longis- 

 simus dorsi. This condition is usually the result of dystokia, 

 where the calf was extracted forcibly. The cow remains down 

 for days or weeks after such a labor, arises then with great 

 difficulty and remains quietly in the stable ; when put out on, 



