In the cow the premonitions of calving are the enlargement of the udder, which becomes firm and resistant to the touch, with more or less swelling in front, and yields a serous, milky fluid; the enlargement and swelling of the vulva, which discharges an abundant, stringy mucus; the drooping of the belly, and the falling in of the muscles at each side of the root of the tail, so as to leave deep hollows. When this last symptom is seen, calving may be counted on in 24 hours or in 2 or 3 days. When the act is imminent, the cow becomes uneasy, moves restlessly, leaves off eating, in the field leaves the herd, lies down and rises again as if in pain, shifts upon her hind feet, moves the tail, and may bellow or moan. 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.