P. G.
PANDE
207
tissue. By the same process of metaplasia,
the periosteum at its outer limit was trans-
formed into bone. The intertrabecular spaces
contained osteoblasts and other cells of the
periosteum. In the region where the perios-
teum still persisted, the subperiosteal tissue
contained numerous osteoblasts, indicating peri-
osteal activity for the formation of new bone.
Histologically, the architecture of the old
compacta showed an abnormal disposition of
young haversian canals.
The formation of
these structures at one part of a section was
found to have proceeded at a high speed, so
that they were closely crowded (Plate XVII, fig.
3), while at other parts no such changes were
discernible. Newly formed haversian canals
were composed entirely of osteoid tissue (Plate
XVIII, fig. 3), which showed poor or no signs of
lamellation and irregular calcification. Certain
areas in the diaphysis, comprising the outer
limit of the old compacta, showed numerous
cement lines indicating active periosteal appo-
sition of bone in which the lamellae were poorly
calcified and the interlamellar spaces traversed
by Volkman's canals. In the course of these
canals young haversian spaces were found to
be developing, and the previous lamellar arrange-
ment giving place to a haversian system of
lamellae formation.
This seemed to have
arisen by osteoclastic resorption of the existing
lamellae, subsequent deposition of osteoid
tissues and finally canalization of this tissue.
A potential haversian canal, appearing in the
osteoid tissue thus formed, contained a conglo-
meration of osteoblasts, and the same cells were
scattered on the osteoid tissue (Plate XVIII,
fig. 3), indicating its osteoblastic origin.
Haversian canals of similar nature and origin
were found in the earlier formed layers of the
exostosis, thus tending to obliterate the line of
demarcation between the newly-formed bone
and the original compacta.
Costal epiphysis
Lesions hitherto undescribed in cattle were
found in the rib epiphysis involving the epiphy-
seal cartilage and the sub-chondral spongiosa.
The proliferating zone of cells in the epiphyseal
cartilage was absent. The zone of preliminary
calcification, which in the normal rib (Plate
XVIII, fig. 2) constitutes a sort of grid-like
arrangement, had disappeared giving place to a
small number of thin and atrophied trabeculae
(Plate XVIII, fig. 4), masses of collagenous
fibrils interspersed with osteoblasts and a few
recently formed trabeculae (Plate XVI, fig. 3).
Apparently these had resulted from extensive
resorption of the original trabeculae by osteo-
clasts or osteoblasts, a subsequent development
of collagenous fibrils and finally the formation
therefrom of young trabeculae.
The collage-
nous tissue from which the young trabeculae
arose, were being transformed into small and
irregular matrices (Plate XVI, fig. 3) resulting
from condensation of the fibrils into homogenous
masses acidophilie in character. These fused
together to form trabeculae in which osteoblasts
of the original tissue still predominated. The
trabeculae thus formed were poorly calcified and
the osteoblasts had acquired lacunar spaces and
were being transformed into osteocytes. These
trabeculae were often irregularly disposed and
their osteoid borders while not abnormal in
width, unlike those of normally calcified trabe-
culae, were irregularly demarcated from the
calcified zone. V. Kossa's method revealed the
axial parts of the trabeculae as irregularly calci-
fied zones (Plate XVII, fig. 4), having rugged
borders against the osteoid tissue. The osteoid
contained few osteoblasts on the surface and a
single layer of similar cells on the free borders.
Lower down in the metaphyseal spongiosa
were found trabeculae which, although poorly
and irregularly calcified, possessed no definite
osteoid borders. Instead, each of them was
closely apposed to a syncytium of osteoblasts,
some of which were enclosed in lacunar spaces.
These tissues appeared to have proliferated,
due to the osteogenic property of the osteo-
blasts, as 'buds' arising from the main syncytial
mass (Plate XVI, fig. 4), were being trans-
formed into bone by a direct process of ossi-
fication. The intertrabecular spaces contained
practically no marrow cells, the chief elements
of the marrow being the reticulum and the
osteoblasts.
Costal diaphysis
Examination showed a considerable resorption
in the cortex and medullary spongiosa. The
former although normal in width, was techni-
cally transformed into a structure composed of
widely separated trabeculae (Plate XIX, fig. 1),
having osteoid borders lined by single layer of
osteoblasts. The medullary spongiosa was
composed of a few unconnected slender trabe-
culae, lined by osteoid tissues of normal width.
Osteoclastic resorption of the trabeculae was also
going on in this region of the bone, and the
intertrabecular spaces, bounded by resorbed
trabeculae, contained disintegrating and a few
intact osteoclasts, numerous osteoblasts mixed
with collagenous fibrils and osseous debris from
resorbed trabeculae.