Femur (Lesser Trochanter)
Long Bone; specifically part of the appendicular skeleton of the lower limb.
Also known as: Thigh Bone (Inner upper bump)
Classification
Long Bone; specifically part of the appendicular skeleton of the lower limb.
Dimensions
This is the largest and heaviest bone in most land mammals. It typically features a long, cylindrical shaft with a ball-shaped top and two rounded knobs at the bottom.
Key Features
Look for the distinct 'ball' on the upper end that fits into the hip. The specific blue-highlighted area is a small, pyramid-shaped bump on the back and inner side of the bone, just below the neck. The bottom end is identifiable by two large, smooth rollers that form part of the knee joint.
Similar Bones
The Humerus (upper arm bone) is often confused with this. To tell them apart, check the top: the thigh bone has a very distinct 'neck' separating the ball from the shaft, whereas the arm bone's ball sits almost directly on top of the shaft. Also, the bottom of the thigh bone has much larger, rounder knobs compared to the flared, flatter end of the arm bone.
Across Species
In humans, this bone is vertical to support upright walking. In horses and rhinos, there is an extra third bump on the outer side for heavy muscle attachment. In birds, it is shorter and air-filled to aid in flight, while in whales, it has shrunk to a tiny, floating vestigial nub that is no longer connected to the rest of the skeleton.
Evolutionary History
The thigh bone first appeared in the lobe-finned fish that began crawling onto land. Over millions of years, it shifted from a horizontal position sticking out from the side of the body—seen in crocodiles and lizards—to a vertical position tucked directly under the body in mammals and dinosaurs, allowing for faster and more efficient movement.
Photography Tips
Capture the bone from the side to show the characteristic curve of the shaft. Use a top-down view of the ball and neck to highlight the unique angles, and place a common object like a coin or ruler next to it to show the scale of the specimen.
Notes
What is the highlighted blue part?