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The cut surface of the tumour presents a deep red or maroon colour. While occasionally met with in tendon sheaths and bursæ, and is then of an orange-yellow colour, the myeloma occurs most frequently in the cancellous tissue at the ends of the long bones, its favourite site being the upper end of the tibia.
The new bone is laid down on the surface, in the Haversian canals, or in the cancellous spaces and medullary canal, or in all three situations.
Among the benign bone tumors are exostoses homologous outgrowths differing from hypertrophies, as they only involve a limited part of the circumference. Barwell had a case of a girl with 38 exostoses. Erichsen mentions a young man of twenty-one with 15 groups of symmetric exostoses in various portions of the body; they were spongy or cancellous in nature.
Short and irregular bones have no medullary canal, only a thin shell of dense bone filled with cancellous tissue. The Right femur sawed in two, lengthwise. Experiment 5. Obtain a part of a beef shin bone, or a portion of a sheep's or calf's leg, including if convenient the knee joint. Have the bone sawed in two, lengthwise, keeping the marrow in place. Boil, scrape, and carefully clean one half.
The X-ray appearances of arthritis deformans necessarily vary with the type of the disease and the joint affected; in the joints of the fingers there is a narrowing of the spaces between the articular ends of the bones as a result of absorption of the articular cartilage, and rarefaction of the cancellous tissue in the vicinity of the joints; in the larger joints there is "lipping" of the articular margins, osteophytes, and other evidence of abnormal ossification in and around the joint.
If the bone is rarefied, the enlarged cancellous spaces are opened into and an eroded and worm-eaten appearance is brought about; with further use of the joint, the bone is worn away, so that in a ball-and-socket joint like the hip, the head of the femur and the acetabulum are markedly altered in size and shape.
Wounds or defects in articular cartilage are repaired by fibrous or osseous tissue derived from the subjacent cancellous spaces. Transplantation of Bone Bone-grafting.
When the new bone is laid down in the Haversian canals, cancellous spaces and medulla, the bone becomes denser and heavier, and is said to be sclerosed; in extreme instances this may result in obliteration of the medullary canal.
If we take a leg bone of a sheep, or a large end of beef shin bone, and saw it lengthwise in halves, we see two distinct structures. There is a hard and compact tissue, like ivory, forming the outside shell, and a spongy tissue inside having the appearance of a beautiful lattice work. Hence this is called cancellous tissue, and the gradual transition from one to the other is apparent.
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