10 



OBSTETRICAL ANA TOMY. 



is joined to the posterior extremity of the sacrum. Their solidity is 

 further assured by a common fibrous sheath which completely envelops 

 them, but without interfering with their mobility. This mobility greatly 

 favours parturition ; but it must be noted that not infrequently the 

 first coccygeal bone is completely ossified with the sacrum, and as this 

 necessarily limits the elevation of the tail, it diminishes the supero- 

 inferior diameter of the posterior opening of the pelvis, and may in this 

 way prove an obstacle to the expulsion of the foetus. 



DiFFEKENCES IN THE PeLVIC AeTICULATIONS OF OTHER AnIMALS. 



In all the domesticated animals other than the Equine species, the 

 sacrum is joined to the last lumbar vertebra by t^iree diarthrodial 

 surfaces only — the head of the body and two transverse inocesses ; these 

 latter on the vertebrae are not in immediate contact with the base of the 



Fig. 5. 



Ligaments of the Lumbar Vertebr.e, Sacrum and Pelvis, seen from below. 



a, Intertransverse Ligament of the Lumbar Vertebrae ; b. Capsular Ligament of 

 the Spinous Process of the Fifth and Sixth Lumbar Vertebrje ; c, Capsular 

 Ligament of the Sacrum ; d, Inferior Sacro iliac Ligament ; e. Obturator 

 Ligament ; /, Transverse Ligament of the Ischio-pubic Symphysis. 



sacrum, an interosseous ligament uniting them. Therefore it is that, 

 in the Coxv more particularly, there is greater mobility in the sacro- 

 lumbar articulation, and the possibility of a greater increase in the 

 supero- inferior diameter of the pelvis when it is subjected to such 

 eccentric pressure as the passage of the foetus would produce. 



Cow. 



In the Cow the ischio-pubic symphysis is considerably longer than in 

 the Mare, not rectilinear, and much curved downwards in the middle ; 

 across this concavity on the floor of the pelvis, the foetus passes during 

 parturition. In the Cow ossification of the symphysis is less complete, 

 and does not take place until much later than in the Mare, though it 

 may in some instances be found entirely accomplished in old animals. 

 Ossification, according to Saint-Cyr, commences in the Cow at the 

 ischial arch, and proceeds forwards ; while in the Mare it begins at the 



