. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 554 OSCAR E. SCHOTTE AND CHARLES B. SMITH The formation of a new callus collar around the diaphyseal shaft is best shown in a cross-section of a thirteen-day-old amputation stage (Fig. 7, Case MCS 1, L-2-III). The outermost layers of osteogenic cells appear to he the largest and most active. Between the outer layer of new hone traheculae and the old bone shaft can he seen perpendicularly arranged trabeculae, cartilage cells, and blood elements. Not indicated in this figure, but nevertheless observable in many sec- tions, is

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Image ID: RHNTFD
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 554 OSCAR E. SCHOTTE AND CHARLES B. SMITH The formation of a new callus collar around the diaphyseal shaft is best shown in a cross-section of a thirteen-day-old amputation stage (Fig. 7, Case MCS 1, L-2-III). The outermost layers of osteogenic cells appear to he the largest and most active. Between the outer layer of new hone traheculae and the old bone shaft can he seen perpendicularly arranged trabeculae, cartilage cells, and blood elements. Not indicated in this figure, but nevertheless observable in many sec- tions, is a final callus that is much larger and of a more amorphous appearance than that typically described for healing in fractures (Ham and Harris, op. cit.).. FIGURE 7. Photomicrograph of a cross-section from a digit (Case MCS 1, L-2-III) fixed thirteen days after amputation, showing the shape and extent of callus formation that follows amputation through the diaphysis. Observe the ring of new tissue formed around the old hone ring. External to the new layer of bone is a layer of large periosteal osteogenic cells. Between the peripheral region of the callus and the old bone new bone trabeculae, cartilage and blood elements are discernible (200 X ). Amputation through and near the spongy epiphysis of the bone results in a different type of callus formation. Heavy proliferation of osteogenic elements is rare and, when found, these collect at the cut surface of the bone nearest to the diaphysis. Few cartilage cells are seen and remodeling appears to take place by osteoclasts and destruction of bone rather than by the formation of new bone trabeculae (Fig. 8, Case MCS 31, L-2-III). Of particular interest in this and in other similar cases is the relative lack of reconstruction within the endosteal surface of the bone (Figs. 7 and 8), its main functions seeming to be confined to hemopoietic activities. Another interesting feature is the observation that the marrow cavity is invaded by co