The effect of neonatal treatment of male mice with antiandrogens and of females with androgens on the development of the os penis and os clitoridis.

The os penis in mice and rats is composed of a proximal intramembranous and endochondral osseous element and a distal cartilaginous, ossifying element. Female mice, but not rats, have a small os clitoridis which corresponds to the intramembranous part of the proximal element of the os penis. In mice of either sex a dense mesenchymatous formation ventral to the urethra is the anlage for the bones of the external genitalia. In the early postnatal period the proximal part of the os penis develops as bone at the outer and as cartilage at the basal end of the anlage, while in females a minute focus of ossification differentiates into the small os clitoridis without passing through a cartilaginous phase. The distal element of the os penis is formed later than the proximal rod and grows at a slower rate. Neonatal treatment with an antiandrogen inhibits the increase in size and calcification of the os penis. Neonatal castration is an even more effective inhibitor. Neonatal treatment with testosterone or dihydrotestosterone, but not with oestradiol, stimulates the growth of the bony proximal os clitoridis, but induces only a rudimentary collagenous distal element. The differences between mice and rats in the response of the tissues of the clitoris to androgenic treatment are discussed, particularly as regards the differentiation of proximal and distal elements.