The bony eminences have generally the name of apophyses; they are
called epiphyses when the cartilage of ossification which unites them
to the bone is not yet encrusted with calcareous substance.
These eminences have four great divisions; viz. those, 1st, of
articulation; 2d, of insertion; 3d, of reflection; 4th, of impression.
1st. The eminences of articulation vary according as the articulation
is moveable or immoveable; I shall not consider them here, as I should
be obliged to repeat it in the chapter upon articulations.
2d. The eminences of insertion are very numerous in the bones; they
only give attachment to the fibrous organs, as the ligaments, the
tendons, the aponeuroses, the dura-mater; no organ differing from these
is implanted into the bony eminences, or generally into the bones,
except by means of them; the muscles are a remarkable example of this.
These eminences are usually much less in women than in men, in children
than in adults, in weak animals than in carnivorous ones who live by
attacking and destroying their prey. The prominence of the eminences of
insertion is always an index of the force and vigour of the motions.
They are the more developed in proportion as the muscles are. Examine
comparatively the skeleton of a strong, sanguineous man, whose muscles
are powerfully delineated through the integuments, and that of a
feeble, phlegmatic man, whose rounded forms like those of women, do not
appear prominent, and you will see the difference.
The form of these eminences of insertion varies greatly; sometimes the
muscles are inserted by many separate aponeurotic fibres; then they
are small, very numerous and form only little asperities imprinted on
a greater or less surface; sometimes it is by a single tendon that the
muscle takes its origin, then the apophysis is usually very prominent,
and occupies a small space. Sometimes a broad aponeurosis gives rise to
the fleshy fibres; it is then a bony line, more or less projecting that
gives insertion.
The eminences are in general in proportion to the muscles that are
attached to them; for example, in three muscles of nearly equal size,
one of which is attached by separate fibres, the other by a tendon, and
the other by an aponeurosis, we observe that the sum of the asperities
of insertion of the first, the separate apophysis of the second, and
the prominent line of the third are nearly equal in the quantity of
osseous substance that forms them; so that by supposing that the
apophysis was divided into asperities, or extended into a line, or that
the asperities were united together, or the line concentrated so as to
form an apophysis, this quantity of osseous substance would be found to
be about the same.
We understand all the advantage of the eminences for the insertion of
muscles, which they render distant from the centre of the bone, lessen
the parallelism with its axis and consequently favour their motions in
an evident manner.
Are these produced by the pulling of the muscles? This opinion borrowed
from the laws of the formation of soft and inorganic bodies, does not
accord with the known phenomena of vitality, with the existence of
eminences where there is no muscular insertion, and which are often
more prominent than these, with the disproportion that exists between
the elongation of certain apophyses by muscular insertion, that of the
styloid, for example, and the force of the muscles that are attached to
it, &c.
The eminences for ligamentary insertion have the advantage, by removing
a little the ligament from the articulation, of facilitating its
motions; this is especially remarkable in the lateral ligaments of the
elbow, the knee, &c.
As to the other eminences of insertion, we can hardly consider in a
general manner their respective functions.
3d. The eminences of reflection are those under which a tendon
passes, in deviating from its primitive course; such is the hook of
the pterygoid apophysis, the malleolar extremity of the fibula, &c.
Almost all these eminences have a slope or excavation in one direction,
connected in the opposite with a ligament, so as to form a ring for the
passage of the tendon.
4th. The eminences of impression are those which arise, when the
different organs form on the osseous surfaces excavations that
separate these eminences, which in fact only appear because the bone
at this place remains at its ordinary level. The cerebral and muscular
impressions are given as examples of this arrangement. But are these
impressions really the effect of the compression of the organs on the
bone, or do they arise from the laws of the osseous development, laws
which give to the bones forms accommodated to the surrounding organs? I
adopt more readily the second than the first of these opinions, which
has been thought very probable from the effect of aneurisms upon bones
that are contiguous to them, which are worn and gradually destroyed
by them. But let us remark that if the muscles, the brain, and the
vessels by their pressure, had upon the bones in a natural state, an
action analogous to that of aneurism, the state of the parts ought to
be the same as in that case. The compact layer ought to be destroyed
where these depressions are, and leave in its place an unequal, ragged
surface, but the contrary happens, which makes me think, that what is
commonly called the impression of organs, is only a natural effect of
ossification.