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42 ANATOMY.
lacuna and its appertaining canaliculi after decalcification, and to obtain
it separate with its included corpuscle." '' It can scarcely be doubted
that the protoplasm of the nucleated corpuscle takes an important share
in the nutritive process in bone, and very probably serves both to mod-
ify the nutritive fluid supplied from the blood and to further its distri-
bution through the lacunar and canalicular system of the bony tissue."^
In flat, thin, or irregular-shaped bones the Haversian canals^' the
lamellpe, etc. are similar to those in the diaphyses of long bones, just
described, though the Haversian system is not so regular in formation.
The Periosteum.
The periosteum is that membrane which covers the greater portion
'^^ ^^^ surfaces of bone, and is composed in a great meas-
Fig 9
ure of fibrillated connective tissue. Between the inter-
lacing of the fibrous bundles lymph-spaces are formed
which contain elementary cellular matter. Although it
is made up of several closely-attached lamella?, for con-
venience of description this structure is divided into two
principal layers, an outer and an inner.
The outer layer is the firmer of the two, being com-
posed mainly of one or more strata of dense white con-
nective tissue, with a few fine yellow elastic fibres inter-
spersed with several lat-cells. Blood- and lymjih-channels
are found in abundance ; the latter anastomose quite free-
ly with those of the inner layer.
The inner or osteogenic layer has its fibrous bundles
more loosely arranged than the outer, and is composed
chiefly of elastic fibres of connective tissue, generally ar-
ranged in several distinct strata. It is much more vas-
The External Peri- cular than the outcr layer, the blood-vessels forming a
"etworlv of ca]-)illaries Avhich anastomose with those of
an(r"uiraeV'''off
^'°""s the outer layer and send numerous oifshoots into the
lium r'*
substance of the bone. In the lower strata of this layer,
or that one next to the bone, especially during the period of formation,
there is a large number of spheroidal or oblong granular cells or cor-
puscles, with oval nuclei, which are usually situated on the side of the
cell. These cells were named osteoblasts by Gegenbauer. The bone-
producing ]iroperty of the inner layer of the periosteum is especially
well marked in the fully-developed inferior maxilla, clavicle, and bones
of the arm and forearm. If the surgeon when operating is careful to
first strip this membrane aside, he can excise or resect a large portion
of bone, the lost tissue being subsequently renewed to a great extent
througli tlie agency of the osteoblasts.
If by disease or otherwise the periosteum be removed from any living
bone, the portion thus denuded generally suffers atrophy, and finally
necrosis. This is not usually the case, however, with the bones of the
cranial vault, as will be hereafter explained.
The periosteum serves as a support to the vessels which supply the
' Qnain's Avatomy.
lacuna and its appertaining canaliculi after decalcification, and to obtain
it separate with its included corpuscle." '' It can scarcely be doubted
that the protoplasm of the nucleated corpuscle takes an important share
in the nutritive process in bone, and very probably serves both to mod-
ify the nutritive fluid supplied from the blood and to further its distri-
bution through the lacunar and canalicular system of the bony tissue."^
In flat, thin, or irregular-shaped bones the Haversian canals^' the
lamellpe, etc. are similar to those in the diaphyses of long bones, just
described, though the Haversian system is not so regular in formation.
The Periosteum.
The periosteum is that membrane which covers the greater portion
'^^ ^^^ surfaces of bone, and is composed in a great meas-
Fig 9
ure of fibrillated connective tissue. Between the inter-
lacing of the fibrous bundles lymph-spaces are formed
which contain elementary cellular matter. Although it
is made up of several closely-attached lamella?, for con-
venience of description this structure is divided into two
principal layers, an outer and an inner.
The outer layer is the firmer of the two, being com-
posed mainly of one or more strata of dense white con-
nective tissue, with a few fine yellow elastic fibres inter-
spersed with several lat-cells. Blood- and lymjih-channels
are found in abundance ; the latter anastomose quite free-
ly with those of the inner layer.
The inner or osteogenic layer has its fibrous bundles
more loosely arranged than the outer, and is composed
chiefly of elastic fibres of connective tissue, generally ar-
ranged in several distinct strata. It is much more vas-
The External Peri- cular than the outcr layer, the blood-vessels forming a
"etworlv of ca]-)illaries Avhich anastomose with those of
an(r"uiraeV'''off
^'°""s the outer layer and send numerous oifshoots into the
lium r'*
substance of the bone. In the lower strata of this layer,
or that one next to the bone, especially during the period of formation,
there is a large number of spheroidal or oblong granular cells or cor-
puscles, with oval nuclei, which are usually situated on the side of the
cell. These cells were named osteoblasts by Gegenbauer. The bone-
producing ]iroperty of the inner layer of the periosteum is especially
well marked in the fully-developed inferior maxilla, clavicle, and bones
of the arm and forearm. If the surgeon when operating is careful to
first strip this membrane aside, he can excise or resect a large portion
of bone, the lost tissue being subsequently renewed to a great extent
througli tlie agency of the osteoblasts.
If by disease or otherwise the periosteum be removed from any living
bone, the portion thus denuded generally suffers atrophy, and finally
necrosis. This is not usually the case, however, with the bones of the
cranial vault, as will be hereafter explained.
The periosteum serves as a support to the vessels which supply the
' Qnain's Avatomy.
