oOO CYCLOPEDIA OP LIVE STOCK AND COMPLETE STOCK DOCTOR. 



the largest in the chest — was easily accommodated in the bis-iliac diameter 

 of the female pelvis, which was greater by 42, 45, 48 and even 52 milli- 

 metres (from iy2 to 2 inches) ; while the sterno-dorsal diameter of the 

 young creatures exceeded that of the sacro-pubic region in the mothers by 

 28, 85, 87, 88 millimetres (from 1 to 31/2 inches). This part of the body of 

 the fa?tus had, therefore, to undergo a corresponding reduction in a ver- 

 tical direction before it could clear the inlet; and even if we take into ac- 

 count the excess of the lateral diameter of the pelvis, it will be found that 

 the thorax and withers of the fojtus still notably exceed in size the opening 

 through which they must pass. That they do pass through it, and with 

 ease in the majority of cases, w^ithout injury to the mother, or the young 

 creature, is a matter of daily experience ; but the mechanism by which the 

 reduction is effected has been much discussed. 



Lafosse endeavored, in the last century, to describe it, and came to the 

 conclusion that the head once through the inlet, the shoulders of the foal, 

 which exceed the withers, pass by their upper part in front of the neck, 

 thus forming a kind of channel which glides along the maternal sacrum; also 

 that the spinous processes of the withers, which are almost cartilaginous, 

 bend back on each other, and to right and left of the spine, thus preventing 

 too great compression of the chest. Altogether, he concluded that the foal, 

 in its passage, becomes moulded in such a manner that the chest has the 

 form of the keel of a ship gliding on the stocks, and in every way corre- 

 sponds to the mother's pelvis, whose internal contour it assumes. 



Rainard, however, takes a slightly different view of this matter; for, 

 while admitting, with Lafosse, the inclination backward of the dorsal spines 

 as a first cause in diminishing the vertebro-sternal or perpendicular 

 diameter of the thorax, he cannot admit that the upper border of the 

 scapula? lie against the neck, but states that the shoulders, on arriving at 

 the pelvic entrance, come in contact with the ascending branches of the 

 ilium, and are thrown back somewhat, leaving the front part of the chest 

 free, and thus diminishing its diameter. He also adds that the withers 

 first enter beneath the sacrum; that the sternum below is pushed back by 

 the anterior border of the pubis, and the chest in this way submits to a 

 process of elongation which notably diminishes its vertical diameter. 



Saint-Cyr agrees with Rainard in this interpretation of the real mech- 

 anism of parturition in the mare. The sternum in being carried back- 

 wards also pulls back the ribs attached to it, and this not only diminishes 

 the chest in a vertical, but also in a horizontal direction, as is witnessed 

 in studying the mechanism of respiration in the living animal, in which, 

 during expiration, the chest decreases in wddth and depth. When the 

 chest is so altered during parturition, the foetus becomes, as it were, elon- 

 gated by this part being depressed : an alteration w^hich occurs all the 

 more readily from the bones composing the thorax being soft and supple, 

 and the organs they enclose (the lungs) not being so developed as they 



