This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The femur serves as a support and keeps the knee out away from the trunk.
The muscles move the thigh on the trunk, or vice versa, and the leg on the thigh.
The blood-vessels and nerves not only supply the structures of the thigh itself, but also serve as channels for the transmission of blood and nervous impulses to and from the parts beyond, hence their large size.