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BONES. — 43
bones Avith blood, these capillaries being assisted bv the niedullaiy
(nutritive) arteries, which pass directly into the bone and are distributed
throughout its system of Haversian canals, until they anastomose with
the branches coming from the periosteum. Thus the bones are per-
meated by the blood and absorbent vessels, a few nerves also entering
their structure. In the bones containing marrow there is an endosteum,
composed of a fine layer of areolar tissue, which lines the medullary
canals and other spaces. This lining membrane is very vascular, and
contains myeloplaxes or osteoclasts. Osteoclasts are also found at the
roots of deciduous teeth when their roots are being absorbed, and in the
lining membranes of bony sinuses. When the periosteum is stripped
from living bone, numerous bleeding spots appear, which indicate the
points where the vessels pass from the membrane into the bone. The
muscles, aponeuroses, tendons, and ligaments are attached to the bone
through the intervention of the periosteum, which is attached to the
bone by its perforating fibres. Tendons and ligaments obtain firm ad-
herence to bones by sending prolongations of their fibre-bundles through
the periosteum.
In inflammation of the bone the periosteum often becomes thickened,
and may be easily removed. At the point of attachment of a muscle
to a bone there is seen a roughening, a depression, or a protuberance
corresponding in size to the strength of the attached muscle.
The Marrow of Bone.
The marrow is a highly vascular, soft tissue situated within all bones.
It fills the medullary canals of long bones, the spaces within spongy
bones, and to a greater or lesser extent the Haversian canals of compact
bone tissue. As a matrix it has a small amount of fine delicate con-
nective tissue woven or interlacing in such a way as to form very thin
septa between the vesicles. Its color and composition vary according
to age and the position it occupies within the bone ; and this difference
has led to its generally being divided into two kinds yelloip and red.
The yellow receives its color from the large number of fat-vesicles it
contains, and is principally found in the medullary canals of long bones
and in small (quantity in some of the cavities of spongy bone. Yellow
marrow is not found in young bones.
The red marrow is dependent for its color on its greater vascularity and
upon its containing red cell-elements independent of the blood it lacks
;
adipose tissue in its substance, and is more fluid than the yellow. Red
marrow is situated in the spaces of spongy bones, especially the bodies
of the vertebra, sternum, the ribs, and diploe of the cranial Ijones.
The vessels of the marrow, which are numerous, are imbedded within
its substance. Their walls are very thin, and they su])ply in part the
adjacent bone as well as tlie surrounding marrow; They anastomose
through the bone with those of the periosteum. Within the marrow
are found a variety of cell-elements (Fig. 10) which vary according to
position and age, and are described as—the mediTllary or true mar-
row-cells; fat-vesicles or adipose-tissue cells; multinuclear giant-cells;
bones Avith blood, these capillaries being assisted bv the niedullaiy
(nutritive) arteries, which pass directly into the bone and are distributed
throughout its system of Haversian canals, until they anastomose with
the branches coming from the periosteum. Thus the bones are per-
meated by the blood and absorbent vessels, a few nerves also entering
their structure. In the bones containing marrow there is an endosteum,
composed of a fine layer of areolar tissue, which lines the medullary
canals and other spaces. This lining membrane is very vascular, and
contains myeloplaxes or osteoclasts. Osteoclasts are also found at the
roots of deciduous teeth when their roots are being absorbed, and in the
lining membranes of bony sinuses. When the periosteum is stripped
from living bone, numerous bleeding spots appear, which indicate the
points where the vessels pass from the membrane into the bone. The
muscles, aponeuroses, tendons, and ligaments are attached to the bone
through the intervention of the periosteum, which is attached to the
bone by its perforating fibres. Tendons and ligaments obtain firm ad-
herence to bones by sending prolongations of their fibre-bundles through
the periosteum.
In inflammation of the bone the periosteum often becomes thickened,
and may be easily removed. At the point of attachment of a muscle
to a bone there is seen a roughening, a depression, or a protuberance
corresponding in size to the strength of the attached muscle.
The Marrow of Bone.
The marrow is a highly vascular, soft tissue situated within all bones.
It fills the medullary canals of long bones, the spaces within spongy
bones, and to a greater or lesser extent the Haversian canals of compact
bone tissue. As a matrix it has a small amount of fine delicate con-
nective tissue woven or interlacing in such a way as to form very thin
septa between the vesicles. Its color and composition vary according
to age and the position it occupies within the bone ; and this difference
has led to its generally being divided into two kinds yelloip and red.
The yellow receives its color from the large number of fat-vesicles it
contains, and is principally found in the medullary canals of long bones
and in small (quantity in some of the cavities of spongy bone. Yellow
marrow is not found in young bones.
The red marrow is dependent for its color on its greater vascularity and
upon its containing red cell-elements independent of the blood it lacks
;
adipose tissue in its substance, and is more fluid than the yellow. Red
marrow is situated in the spaces of spongy bones, especially the bodies
of the vertebra, sternum, the ribs, and diploe of the cranial Ijones.
The vessels of the marrow, which are numerous, are imbedded within
its substance. Their walls are very thin, and they su])ply in part the
adjacent bone as well as tlie surrounding marrow; They anastomose
through the bone with those of the periosteum. Within the marrow
are found a variety of cell-elements (Fig. 10) which vary according to
position and age, and are described as—the mediTllary or true mar-
row-cells; fat-vesicles or adipose-tissue cells; multinuclear giant-cells;
