196 DISEASES OF THE HORSE, 
back. AIl this suggests the development of extra parts from the 
same primary layer of the impregnated and developing ovum. The 
effect of disturbing conditions in giving such wrong directions to 
the developmental forces is well shown in the experiments of St. 
Hilaire and Valentine in varnishing, shaking, and otherwise break- 
ing up the natural connections in eggs, and thereby determining the 
formation of monstrosities at will. So, in the mammal, blows and 
other injuries that detach the fetal membranes from the walls of the 
womb or that modify their circulation by inducing inflammation are 
at times followed by the development of a monster. The excitement, 
mental and physical, attendant on fright occasionally acts in a simi- 
lar way, acting probably through the same channels. 
The monstrous forms liable to interfere with parturition are such 
as, from contracted or twisted limbs or spine, must be presented 
double; where supernumerary limbs, head, or body must approach 
the passages with the natural ones; where a head or other member 
has attained to an unnatural size; where the body of one fetus has 
become inclosed in or attached to another, etc. 
Extraction is sometimes possible by straightening the members 
and obtaining such a presentation as will reduce the presenting mass 
to its smallest and most wedgelike dimensions. To effect this it 
may be needful to cut the flexor tendons of bent limbs or the muscles 
on the side of a twisted neck or body; one or more of the manipu- 
lations necessary to secure and bring up a missing member may be 
required. In most cases of monstrosity by excess, however, it is 
needful to remove the superfluous parts, in which case the general 
principles employed for embryotomy must be followed. The Cesa- 
rean section, by which the fetus is extracted through an incision in 
the walls of the abdomen and womb, is inadmissible, as it prac- 
tically entails the sacrifice of the mare, which should never be done 
for the sake of a monster. (See “ Embryotomy,” p. 202.) 
ENTRANCE OF TWINS INTO THE PASSAGE AT ONCE.—T wins are rare in 
the mare, and still more rare is the impaction of both at once into 
the pelvis. The condition would be easily recognized by the fact 
that two fore limbs and two hind would occupy the passage at once, 
the front of the hoofs of the fore feet being turned upward and 
those of the hind feet downward. If both belonged to one foal, they 
would be turned in the same direction. Once recognized, the con- 
dition is easily remedied by passing a rope with a running noose 
round each foot of the foal that is furthest advanced or that prom- 
ises to be most easily extracted, and to push the members of the 
other fetus back into the depth of the womb. As soon as the one 
fetus is fully engaged into the passage it will hold its place and its 
delivery will proceed in the natural way. 
