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14 OBSTETRICAL ANATOMY. 



5 . Sacro-coccygeal Articulations. 



These resemble those of the vertebras in general : there being a thick 

 disc of fibro-cartilage placed between each tail-bone, the first of which 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 favors 

 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. 



Differences in the Pelvic Articulations of other Animals. 



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

 sacrum is joined to the last lumbar vertebra by three diarthrodial sur- 

 faces only : the head of the body and two transverse processes ; these 

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

 the sacrum, an interosseous ligament unites them. Therefore it is that, 

 in the Cow more particularly, there is greater mobility in the sacro-lum- 

 bar 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-puhic symphysis is longer than in the Mare, not 

 rectilinear, and much curved downwards in the middle ; across this con- 

 cavity 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 pubis and extends back- 

 wards. The same authority remarks that this symphysis in the Cow has 

 often a salient crest projecting *into the pelvic cavity, and which, if 

 it does not offer a very considerable obstacle to the passage of the foetus, 

 may nevertheless greatly fatigue the obstetrist when his hand is engaged 

 between it and the young creature, during the straining of the mother. 



Sheep and Goat. 



In these animals the. ischio-pubic symphysis is rectilinear; the inter- 

 posed cartilage is not ossified until very late in life, and almost never in 

 those which have had many young. The same remarks are applicable 

 to this symphysis in the Pig. 



JBitch and Cat. 



The symphysis in the Bitch and Cat scarcely ever ossifies ; so that 

 these animals, when advanced in age, still have a notable degree of 

 mobility in this region, and the diameter of the pelvic cavity may be 

 proportionately increased. 



Sacro-sciatic Ligament. 



The sacro-sciatic ligament (Fig. 4, d) transforms the pelvic cavity into a 

 complete canal by filling up the space on the side of the pelvis, between 



