906 
which the fetus attains a size utterly incom- 
patible to pass through the small pelvis of the 
mother were it not for the extraordinary elas- 
ticity of the pubic ligament, being capable of 
allowing the ends of the pubic bones to diverge 
from each other to the distance of nearly an 
inch and a half. The capability of the pelvis 
being enlarged by this fos, a depends upon 
the shortness of its transverse, and the great 
length of its antero-posterior or sacro-pubal 
diameter, the ossa innominata running forwards 
from each side of the sacrum ina nearly parallel 
direction, or rather forming an isoskeles triangle, 
its apex at the pubes, its base at the sacrum. 
This greater length of the antero-posterior to 
that of the transverse diameter may be traced 
with few exceptions along the whole chain of 
pelviferous vertebrata until we reach the human 
subject, and even here, until the age of puberty, 
we find a similar relation between these dia- 
meters. This form of pelvis is eminently 
adapted for dilatation during parturition; the 
ossa innominata, moving, as it were, upon a 
hinge at their sacro-iliac synchondroses, are 
capable of a considerable separation at their 
pubic ends, by which means the pelvis is 
greatly enlarged and passage of the fetus much 
facilitated. 
In some animals, as cows, the swelling and 
softening of the ligamento-cartilaginous unions 
is distinctly seen on the approach of labour, 
the lumbar vertebra and sacrum sinking be- 
tween the ilia, and these bones “ slipping,” as 
it is called, over each other at their sacro-iliac 
i tes as the animal moves her hind legs. 
e axis of the pelvis in animals being with 
few exceptions parallel with the spine, and the 
outlet from the formation of the sacrum being 
so large, it will be seen that up to the Rumi- 
nantia the mechanism of parturition is extremely 
simple, the more so as until we reach this class 
the uterus in great measure preserves its tubu- 
lar formation, rendering it next to impossible 
that the foetus should come in any other direc- 
tion than with its long diameter corresponding 
to the axis of the canal through which it has to 
s. 
In the Marsupiata the foetus is expelled at so 
early a stage of developement, and is therefore 
so small, that little or no dilatation of the pelvis 
is required ; in these animals we see the pelvis 
well developed, and the difference between the 
length of the transverse and antero-posterior 
diameters inconsiderable : in them it is probable 
that litle or no separation of the pubic bones 
takes place during parturition. 
In the other and higher classes of the Mam- 
malia the hard and well developed head of the 
foetus and its inflexible limbs, especially in the 
Ruminantia,as also the horse, ass, &c., present 
very considerable obstructions to its passage 
through the pelvis, and require that it should 
take a certain position during labour in order 
that it may be born with such a degree of faci- 
lity and within such a period of time as shall 
not endanger its own life or that of its mother. 
Although the pelvis among the higher Mam- 
malia still presents many remarkable points 
of difference from that of the human race, least 
PARTURITION. 
pothens in the Quadrumana, still on the other 
and the mechanism of parturition in these 
animals resembles in many respects this process 
in man. The embryo has a somewhat similar 
position in the pa as ae ry the human 
subject. In the early periods of pregnancy in 
both cases, the limbs ond off rian the trunk, 
whereas in the latter months they are 
close to the body. The lower extremities or 
hind legs in animals are always turned upon ~ 
the abdomen ; in some instances the knees are 
bent, in others not. 
The arms of the child are crossed upon the 
breast; in animals the forelegs are usually 
placed along the side of the head and generally 
a little below it; it is rare that one or both are 
found above the head, although it has some- 
times occurred that the two forelegs have been 
found crossing each other over the head. The 
forelegs are seldom found bent down under the 
abdomen. 
The embryo usually lies upon its belly, or 
on one side; and from being scarcely ever 
found upon the back it may be presumed that 
this position is very rare.* The head is mostly 
turned towards the os uteri, although cases are 
by no means uncommon, even among the larger 
animals, of its being turned to the fundus uteri. 
In the larger animals (mare, cow, sheep, goat, 
&c.) the embryo at first lies tolerably uncon- 
strained, whereas at a later period it descends — 
into the smaller part of the uterus, and hence at — 
this time we usually find the nose bent down 
upon the breast. In the child this position 
with the chin upon the breast exists from a very 
early period. 1g 
In the smaller animals, viz. the dog, cat, rat, 
&c., the head at the end of pregnancy mostly 
lies flat on the lower jaw, and therefore presents — 
with the nose, whereas in the larger animals — 
the occiput presents, and this probably with- 
draws again as labour comes on. ears 
are always pressed close to the head, being 
turned either forwards or backwards; they are 
usually found bent forwards in the dog, cat, 
and horse, and backwards in the cow, sheep, 
goat, rabbit, hare, &c. 
Although the human foetus usually prese 
also with the head, the whole mechanism of it 
parturition is very different from that of the ani 
mals above-mentioned ; the angles of the pelvi 
axes with the spine and with each other, 
the relative size of the antero-posterior a 
transverse diameters, are so different that ¥ 
find the greater part of the process subservit 
to laws which do not exist in the lower animals 
nevertheless the grand primary law with whic 
we commenced holds equally good in the hu 
man subject as in the lowest ovipara, and uj 
this depends the great distinction betwe 
natural and unnatural presentations; for so lo 
as the long diameter of the child is par 
with the axis of the passage through whi 
comes, the child will present with its cephalk 
or its pelvic extremity, and can be born in that 
position ; whereas if its long diameter does mt 
correspond with that of the axis of the pel 
* Joerg. 
