The osseous cavities are very numerous; those only which are found
on the exterior of the bones will be treated of. They are divided,
like the eminences, into articular and non-articular. The first
will be examined, with the analogous eminences, in the chapter on
articulations. Among the second there are cavities, 1st, of insertion;
2d, of reception; 3d, of slipping; 4th, of impression; 5th, of
transmission; 6th, of nutrition.
1st. The cavities of insertion give attachment to the aponeuroses of
the muscles, to the ligaments, &c. They have the advantage, 1st, of
multiplying the insertions of the fibres, without increasing the size
of the bone, since a concave surface is evidently more extensive than a
plain surface would be which should occupy the space between its edges;
2d, of allowing the muscular fibres more room, and consequently giving
them greater length than if they arose from an eminence, which also
gives more extent to the motions. The pterygoid, digastric cavities,
&c. present examples of this arrangement.
2d. The cavities of reception are those which serve to receive an
organ, lodge and defend it; such are the fossæ of the bones of the
cranium, those of the ossa ilii, &c. These cavities sometimes belong to
the whole of the bone, the form of which is concave, as we see in the
frontal bone, sometimes they are hollowed out upon an insulated part,
like the maxillary depression of the inferior jaw; they are always
destined for an essential part, for a gland, a viscus, &c.
3d. The cavities of slipping are in general found at the extremity
of the long bones. They are grooves, more or less deep, in which the
tendons glide to go to the place in which they are inserted. All are
covered with a cartilage and terminated by a very strong ligamentary
ring. Do the tendons by their friction form these cavities? This is
the common opinion, but it does not appear to me more probable than
the theory of muscular, vascular impressions, &c. These cavities
ought to be then so much the deeper, in proportion as the muscles
are the more exerted; they ought not to exist in subjects paralytic
from their infancy; they ought not to exist in the cartilages of
ossification in the fœtus, whose limbs have hardly ever moved; but the
contrary of all this is constantly observed. Let us describe then all
the different configurations of the bones, as a consequence of the
laws of ossification, laws in obedience to which the osseous forms,
all primitively determined, are made to develop. The size of the
extremities of the long bones favours the existence of these different
cavities, which cannot on this account injure the osseous solidity.
4th. The cavities of impression correspond with the eminences of the
same name. I have spoken of them above.
5th. The cavities of transmission are especially destined for the
vessels and the nerves. We find many of them on the head; they have
sometimes the form of a groove, sometimes that of a tube and at others
that of a slit, according to the thickness or breadth of the bones
which these vessels or nerves traverse in order to go from one place to
another. The periosteum lines them; they contain more or less cellular
texture. The nerves and vessels they transmit are foreign to the bones.
6th. The cavities of nutrition, on the contrary, give passage to
vessels which carry to the bones or the medullary organ the substances
that repair them. They are of three sorts.
The first form canals that are seen on the long bones exclusively,
and go to the medullary cavity. Each bone has but one of these,
situated always on its body, directed obliquely between the fibres of
the compact texture, running sometimes from below upwards, sometimes
from above down into the cavity of the bone, and thus forming a
communication from without to within for the vessel of the medullary
organ. This foramen serves particularly for the exhalation and
nutrition of this organ, and nourishes the bone only secondarily.
The second kind of cavities of nutrition belong especially to the
texture of the cells of the bones. Thus they are seen wherever
this texture abounds, in the extremities of the long bones, the
circumference of the flat ones, and the whole superficies of the short
ones. Their diameter is greater than that of the canal which goes to
the medullary cavity; it is less than that of the canals of the compact
texture. Their number is very considerable; I have counted a hundred
and forty upon the tibial extremity of the femur, twenty upon the body
of one of the dorsal vertebræ, fifty upon the os calcis, &c. In general
this number is always in proportion to the quantity of the texture of
the cells that the bone contains. Hence why there are but few on the
flat bones of the cranium, why they are more numerous on the flat bones
of the pelvis especially where this texture is abundant, as on the
ischium, on the iliac portion of the circumference of the ilium, &c.
By pouring mercury into the spongy texture, it runs out from all these
foramina, and thus proves their communications. They are irregularly
scattered wherever they are. They are not met with on the body of the
long bones, because the body contains little or none of the texture of
the cells.
The third kind of canals of nutrition is only destined to the compact
texture. It consists of an infinite number of little pores which the
eye can clearly distinguish, and through which small vessels pass, that
go to this texture. An evident proof that they do not go to the texture
of the cells, is, that in the preceding experiment, the mercury never
finds in them a way to escape externally. It is impossible to determine
their number; it is prodigious in childhood. As the bones in old age
become filled with calcareous substance, they are obliterated, and
the vessels they contain become small ligaments, foreign to osseous
nutrition, which continually grows weaker, and is soon annihilated,
and allows necrosis to seize upon the bones, if general death does not
prevent this partial death of the osseous system.