234 



NORMAL PARTURITION. 



the withers towards the sacrum. When perfectly natural, the head and 

 fore legs first enter the inlet ; the head is extended, forehead looking 

 upwards to the sacrum, chin towards the pubis, nose forward, the lower 

 jaw resting on the outstretched limbs, the feet of which extend a little 

 beyond the nose. Then comes the neck, and after it the chest and 

 shoulders, which arrive at the inlet w^hen the nose and feet show them- 

 selves at the rulva. 



In this course it will be observed that, so far as the head and limbs are 

 concerned, there is no difficulty, as the pelvic diameter readily admits 

 them when the soft parts are sufficiently relaxed. With the chest, how- 

 ever, there is difficulty, as its diameter is greater than that of the pelvis ; 

 and the question is, therefore, how it is got through the canal. In 1870, 

 Saint-Cyr saw four well-bred harness and saddle Mares give birth to foals 

 at tiie Lyons Veterinary School. Gestation had been regular, and par- 

 turition, which was easy and favorable, did not exceed the ordinary dura- 

 tion. In taking the diameters of the maternal pelvis by the method al- 

 ready described, and those of the foetus (dorso-sternal, biscapulo-humeral, 

 and bicoxo-femoral), it was found that in these four instances the biscap- 

 ulo-humeral diameter — the largest in the chest — was easily accommo- 

 dated in the bis-iliac diameter of the female pelvis, which was greater by 

 42, 45, 48, and even 52 millimetres (from i^^ 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 i to 3^ 

 inches). This part of the body of the foetus had, therefore, to undergo a 

 corresponding reduction in a vertical direction before it could clear the 

 inlet; and even if we take into account the excess of the lateral diameter 

 of the pelvis, it will be found that the thorax and withers of the foetus 

 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, 

 wdthout 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, wdiich are almost cartilagi- 

 nous, 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 corresponds 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 vertebrc-sternal or perpendicular 

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

 scapulae 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. 



