. Quain's elements of anatomy . ; p, fibrous layer of theperiosteum ; o, layer of osteo-blasts, some of them are em-bedded in the osseous layer asbone corpuscles in lacunce ; hi,blood-vessels occupied by blood-corpuscles. B, beyond the lineof ossific advance the periosteummay be noticed to be distinctlyincurved. This incurvation isgradually moved on, the cartil-age expanding behind it untilthe head of the bone is reached,when it forms the periostealnotch or groove represented infig. 105, p. At a short distance below the advancing ossification, the medullaryspaces become at first somewhat more
. Quain's elements of anatomy . ; p, fibrous layer of theperiosteum ; o, layer of osteo-blasts, some of them are em-bedded in the osseous layer asbone corpuscles in lacunce ; hi,blood-vessels occupied by blood-corpuscles. B, beyond the lineof ossific advance the periosteummay be noticed to be distinctlyincurved. This incurvation isgradually moved on, the cartil-age expanding behind it untilthe head of the bone is reached,when it forms the periostealnotch or groove represented infig. 105, p. At a short distance below the advancing ossification, the medullaryspaces become at first somewhat more enlarged by further absorption,but at the same time their walls (which were at first formed onlyby the remains of the walls of the primary areolae and thereforeonly by calcified cartilage-matrix) begin to be thickened by thedeposition of layers of new bone, and this deposition increases graduallytowards the middle of the shaft (compare fig. 108, c and d). Thelacunae first appear in this deposit, there are of course none in the. OSSIFICATION IN CARTILAGE. 109 calcified cartilage. Moreover as layer after layer is deposited upon thewalls of the medullary spaces these become gradually narrowed into Fig. 105.—^LoNaiTtJDiNAL SEC- Fig. 105. TION THKOTJGH THE UPPERHALF OP THE DECALCIFIEDHUMEEUS OFAFCETAL SHEEP,ASSEEN UNDER AMAGNIFTINGPOWER OF ABOUT 30 DIAME-TERS. (Drawn by ]\Ir. ) (E. A. S.) ic, the parb of the shaftwhich was primarily ossifiedin cartilage ; what remains ofthe primary bone is repre-sented as dark, enveloped bythe clear secondary areolcC of the bone areoccupied by embryonic mar-row with osteoblasts, andblood - vessels variously cut,represented as dark long straight vessel {bvpasses in advance of the lineof ossification far into thecartilaginous head, most ofthe others loop round close tothe cartilage. At one or twoplaces in the older parts ofthe bone elongated groujis ofcartilage-cells (c) may still beseen which have escaped ab-sorptio
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