Involution of placental site and corpus luteum in the monkey

Fibrous and often calcified myometrial nodules up to 0.4 cm. in diameter were observed in the majority of parous monkeys at necropsy. Histologically, these areas consisted of large pale cells surrounding thickened blood vessels. Frequently, the cells were seen inside thrombosed blood vessels. Fibrosis was common. These nodules are considered to be involuting placental sites which, in monkeys, may persist for more than one year post partum while in human beings they have disappeared by 7 weeks post partum. The origin of the large cells is disputed, but they may be decidual. In the ovaries, histiocytic corpora lutea predominated rather than the corpora albicantia usually seen in human beings. The histocytic coropora contained a ceroid pigment. It is concluded that the development of corpora albicantia from corpora lutea via corpora histiocytica takes longer in monkeys than in man.