10 HEALTHY ANATOMY.
"It follows that in the usual impaction of the neck of
the femur, the anterior wall refuses to be impacted. The
posterior wall, on the contrary, is deeply imbedded into its
own substance, offering little or no resistance to the force
producing the fracture. The impaction, therefore, takes
place exclusively on the posterior aspect of the neck, while
the anterior and thick wall, acting as a hinge at the point
of fracture, allows the outward rotation of the shaft, so
constantly observed in these cases.
"In making these sections, another anatomical peculi- arity will be observed, provided the bone is healthy, and well developed. This will be best seen in the new speci- men. Let the small trochanter, the intertrochanteric line, and the back part of the great trochanter be removed with a fine saw, in one piece. By getting rid of this projecting mass, the back of the neck may be brought into a continu- ous curve with the back of the shaft. The part removed will be found to be merely a buttress of spongy tissue, built out for the attachment of the muscles, while the true neck of the femur will be discovered beneath the removed portion, uniting the back of the neck continuously with the true shaft below.
"This true neck may be demonstrated by lightly scrap- ing out, with a rougine, the cancellar structure, until the instrument is arrested by the firm wall beneath. This last is the true neck, and offers some slight resistance to the impaction of the posterior wall. On the last section, in the preparation first described, this true neck will be seen as a very thin line, continuous with the posterior wall of the neck, plunging beneath the intertrochanteric line, or buttress, and passing towards a point corresponding with the middle of the outside of the shaft. Before reaching this, however, it loses itself in radiating spokes or fibres, which, though quite slender, seem intended to contribute by their mechanical arrangement, a little towards the strength of the bone.
"After examining these preparations, it will be readily seen why the impaction is so exclusively upon the back of the neck, producing outward rotation, and why it not un- frequently splits off the small trochanter, and the intertro-
