Overview
The os penis is a heterotopic bone (part of the visceral skeleton) that develops within the corpus cavernosum of the glans penis. It is long and fairly straight, with a broad caudal base and a tapering cranial apex prolonged by fibrocartilage. It keeps the penis rigid during intromission, before full erection.
Key features
- Urethral groove (sulcus urethrae): deep groove on the ventral surface that lodges the penile urethra and the corpus spongiosum. It is widest at the base and becomes shallower towards the apex.
- Base: caudal, thick end, continuous with the corpus cavernosum.
- Apex: cranial, thin end, ending in a fibrocartilaginous tip inside the glans.
Clinical relevance
- Urethral obstruction: urinary stones (struvite, oxalate, urate, cystine) often lodge just caudal to the os penis, where the urethra cannot expand inside the bony groove. A urethrostomy (scrotal or prescrotal) bypasses this narrow segment.
- Fractures of the os penis are rare; they can cause pain, haematuria and urethral stricture.
- On radiographs the os penis and its groove must not be confused with stones or mineralisation.
In this model the os penis comes from a 3D scan of an isolated specimen (Sketchfab), scaled to this skeleton; its position in the ventral abdominal wall is approximate.