Femur is the Latin name for the bone of the thigh; a name that anatomists have preserved. It is called μηρὸν [thigh] in Greek.

This bone is the largest and the strongest of the cylindrical bones: it carries itself from outside to inside. The femurs are isolated from each other at the top; they almost touch near the knees. One of the principle advantages of this is that it gives more speed and security in our step. If the femurs had been parallel, our body would have had to form a partial circle with each stride and our center of gravity would have been too much in danger of not being supported. To ensure that femurs , which extend obliquely towards each other, can be supported by the [lower] legs—which are situated perpendicularly—their lower end is slightly curved in to out.

The lower part of the femur has a big and polished head, in which a spongy cavity can be observed: in this spongy cavity is an attached ligament improperly called the round ligament . This more unbound part below the head, called the neck of the femur bone , has a large number of holes, into which, according to some, some feeding vessels penetrate, and according to others, the fibers of a strong, round ligament attach to a harsh edge, which is at the root of the neck. This ligament contains and subjects the entire joint; the obliquity of the neck, which is almost horizontal, increases the spreading of the femurs , which we have already discussed, and gives a more favorable position for the muscles, which are in this region further from the fixed point, and some of which work by an angled lever, the neck of the femur making an obtuse angle with the rest of the bone which points downward.

The upper part of the femur has two processes, which are, like the head, only epiphyses at a young age; these processes are called trochanters : one is large and lateral and the other is small and medial. These two processes received the name trochanters because they serve as the insertion site of those muscles, which are the principle instruments for thigh rotation movement, or else because the rotary motion there is more sensitive than it is in the body of the femur .

The lower end of the femur is much bigger than any other of its parts: it forms two tuberosities called condyles , separated by a considerable cavity, and it is articulated by a hinge joint with the tibia. Here lie two cavities: the anterior one is for free rotary movement; the posterior is where the femoral vessels are wrapped in fat. Sesamoid bones are sometimes found on these condyles, mainly on the outside. We will say nothing of muscles and ligaments that attach to the end of the femur bone, which is only an epiphysis in its young stage.

What is most singular about the body of the femur bone is its curvature. It is convex outwardly and vaulted from behind; the purpose and cause of this curvature are quite unknown. It seems that two remarks escaped the authors who have described it: the first, that the largest angle of this curvature is closest to the upper part of the femur , which one could attribute to the resistance of the kneecap, against which this bone braces; perhaps even the curvature of the femur is produced by weight of the body in children who bend down and cannot bend at their knee.

The second remark is that the body of the femur seems to be twisted in some manner; a plane that would pass through the centers of the two condyles and by the middle of the bone, would make a very remarkable angle with another plane that would pass through the same middle and by the centers of the head of the femur and the major trochanter .