PARTURITION, 



501 



are immediately afterwards; so that a moderate amount of pressure, pro- 

 vided it is not too long continued, may be borne with comparative impunity. 



In the larger animals the pelvis cannot undergo any sensible increase 

 in size during the passage of the deepest portion of the foetal body through 

 the inlet, which is, in the mare, an absolutely inextensible bony girdle. 

 Lafosse has sawn through the pubis of mares about to foal, and he found 

 that during parturition there was only a space of two lines between the 

 sawn margins. So that it is the body of the foetus which has to accommo- 

 date itself to this part of the passage at this stage of delivery. 



When, however, it has passed through the inlet, extiensibility of the 

 maternal tissues can, and does, take place, and permits an enlargement 

 of the canal. The wide sacro-ischiatic ligaments, which enclose the pelvis 



ANTERIOR PRESENTATION ] EXTREME DOWNWARD DEVIATION OF THE HEAD. 



laterally, are softened and more elastic during birth; the sacro-iliac and 

 sacro-lumbar articulations are increased in mobility; and even the pos- 

 terior part of the ischio-pubic symphysis may become slightly relaxed. So 

 that when once approaching the outlet the progress of birth is more rapid, 

 and this progress may be aided if, as is pointed out by Lafosse, the tail of 

 the animal is well elevated. 



A slight check to expulsion is observed (especially in the mare) when 

 the croup arrives at the inlet, as this part nearly corresponds in diameter 

 to this opening, being, if anything, slightly less. However, notwithstand- 

 ing this, in consequence of the croup being less susceptible of diminution 

 than the chest, and although the bones may yield to some extent, friction 



