Its been nourished by the food the mother takes which is been converted into a liquid substance and later sent to the embryo through the placenta

You would think that a chubby person is well-nourished, but that's not necessarily true. Of course it is obvious that a person grossly underweight is malnourished. A well-nourished person is one who is eating the righ kinds and quantities of food. You can't really tell a well-nourished person always by his looks. Blood work will often tell you more.

how are the bones in the body nourished

The act of nourishing, or the state of being nourished; nutrition., That which serves to nourish; nutriment; food.

Nourishment means all the food and nutrients you need in order to live and survive. If you are under nourished, that means you are not getting enough food or nutrients.