"There are in this body head-hairs, body-hairs, nails, teeth, skin, flesh, sinews, bones, marrow, kidneys, heart, liver, pleura, spleen, lungs, intestines, intestinal tract, stomach, feces, bile, phlegm, pus, blood, sweat, fat, tears, grease, saliva, nasal mucus, synovium (oil lubricating the joints), urine, and brain in the skull." source

This seems like a pretty comprehensive list, but semen and menses are noticeably missing; although if they were included, there would obviously have to be separate male and female versions of this contemplation.

Do we know why they are missing? Are other body parts missing? It seems unusual given how direct the Buddha's teachings normally are; so I imagine there is a reason. Thank you!