M ECU A MS. M or I'AirrriilTKiX. 251 



Make. 

 Anterior Presentation. 



1. Mechanism of Parturition in the Dorso-sacrai Positio)i. — In this 

 position it has been stated that the foetus presents simultaneously with 

 the head and fore limbs, the back directed to that of the mother and 

 the withers towards the sacrum. Wlien perfectly natural, the head 

 and fore lej,'s first enter the inlet ; the head is extended, forehead look- 

 ing upwards to the sacrum, cliin towards the pul)is, 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 when the nose and feet show 

 themselves at the vulva. 



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

 are concerned, there is no dilViculty, as tlie pelvic diameter readily admits 

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

 ever, there is dilliculty, 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 iiarness and saddle Mares give 

 birth to Foals at the Lyons Veterinary School. (Jestation had been 

 regular, and parturition, which was easy and favourable, did not exceed 

 tlie ordinary duration. In taking the diameters of the maternal pelvis 

 by the method already described, and those of the fcetus (dorso-sternal, 

 biscapulo-humcral, and bicoxo-femoral), it was found that in these four 

 instances the biscapulo humeral diameter — the largest in the chest — was 

 easily accommodated in the bis-iliac diameter of the female pelvis, which 

 was greater by i'2, 45, -48, and even 52 millimetres (from li to 2 inches) ; 

 while the sterno-dorsal diameter of the young creatures exceeded that 

 of the sacro-pubic region in the mothers by 2.S, 85, 87, 88 millimetres 

 (from 1 to S\ 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 fu'tus still notably exceed in size theoj)ening through which they 

 must pass. That they do pass through it, and with ease in the majority 

 of cases, without 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 endeavoured, 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 

 sacnnn ; also that the spinous processes of the withers, wliieh are almost 

 cartilaginous, bend back on eacli other, and to right and left of the spine, 

 thus preventing too great compression of the chest. Altogether, he con- 

 cluded 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, the internal contour 

 of whicli 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 tirst cause in diminishing the vertebro-sternal or perpendi- 

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

 the scapuUr lie against the neck, but states that theshoulders, on arriv- 



