Uterus Didelphys with Hysterolith.
Segmental aplasia of the left uterine horn and complete duplication of the cervix (uterus didelphys). There is an occluding obstruction at the base of the left horn which trapped uterine secretions. Here the secretions are inspissated and have formed a hysterolith (uterine stone; uterine "pebble" in this case?). The corpus luteum is retained for lack of a signal from the ipsilateral horn (prostaglandin F2alpha) to regress. The cow appears to have been pregnant in the right horn.
Roberts SJ (1973)