n. When labor pains come on
the back is arched, the croup drooped, the belly is drawn up, and straining
is more or less violent and continuous. Meanwhile blood may have appeared
on the vulva and tail, and soon the clear water bags protrude between the
lips of the vulva. They increase rapidly, hanging down toward the hocks,
and the fore or hind feet can be detected within them. With the rupture of
the bags and escape of the waters the womb contracts on the solid, angular
body of the fetus and is at once stimulated to more violent contractions,
so that the work proceeds with redoubled energy to the complete expulsion.
This is why it is wrong to rupture the water bags if the presentation is
normal, as they furnish a soft, uniform pressure for the preliminary
dilation of the mouth of the womb and passages, in anticipation of the
severe strain put upon them as the solid body of the calf passes.

The cow often calves standing, in which case the navel string is broken as
the calf falls to the ground. If, however, she is recumbent, this cord is
torn through as she rises. The afterpains come on 3 or 4 hours later and
expel the membranes, which should never be left longer than 24 hours.

NATURAL PRESENTATION.

When there is but one calf the natural presentation is that of the fore
feet with the front of the hoofs and knees turned upward toward the tail of
the dam and the nose lying between the knees. (Pl. XV.) If there are twins
the natural position of the second is that of the hind feet, the heels and
hocks turned upward toward the cow's tail. (Pl. XVIII, fig. 1.) In both of
these natural positions the curvature of the body of the calf--the back
arched upward--is the same with the curvature of the passages, which
descend anteriorly into the womb, ascend over the brim of the pelvis, and
descend again toward the external opening (vulva). Any presentation
differing from the above is abnormal.

OBSTACLES TO PARTURITION.

With a well-formed cow and calf and a natural presentation as above,
calving is usually prompt and easy. Obstacles may, however, come from
failure of the mouth of the womb to dilate; from twisting of the neck of
the womb; from tumors in the vagina; from dropsy in the womb or abdomen;
from overdistention of the rectum or bladder; from undue narrowing of the
passages; from excess of fat in the walls of the pelvis; from the
disturbance of a nervous cow by noises; from stone or urine in the bladder;
from wrong p