Patterns of vascular channels in the cortex of the human mandible.

The plan and organization of vascular channels of cortical bone are best known for the shafts of mammalian long bones where numerous elongate parallel vessels either have cross connections or branch and anastomose to form a complex threedimensional mesh with a predominant proximo-distal orientation (Petersen, '30; Schumacher, '35; Ruth, '47; Bartoli and Vasciaveo, '57; Cohen and Harris, '58). The pattern is roughly comparable to that seen in carmine-gelatin injected striate muscle; in muscle, the intervascular tissue consists largely of muscle fibers and endomysium; in bone it consists of osseous lamellae and osteocytes. A recent technique (Knapp, Avery and Costich, '58; Avery and Knapp, '59; Avery, Knapp and Dempster, '59) has made it possible to see the cortical vascular channels of whole bones or of large pieces of them. The technique, in its simplest form, requires: (1) deorganifying a large piece of cortical bone (i.e., removing cells, fibers and ground substance) by leaching in ethylenediamine, (2) filling cortical channels with India ink, (3) removing dried surface carbon by a jet of abrasive and ( 4 ) clearing in styrene. In much the way that the orientation of the xylem and xylem fibers in wood results in a linear "grain" pattern, the vascular channels and osteones produce a grain in cortical bone. As in wood the mechanical properties of bone differ in a direction along and across the grain (Dempster and Liddicoat, '52), the grain pattern of various bones has been most clearly demonstrated by the Benninghoff split-line technique. When pointed awls with a circular cross section are pushed into decalcified cortical bone and withdrawn, the holes close to form longitudinal crevices which, when touched with ink, show as blackened lines. When successive puncture marks that are aligned are interconnected, the grain of the bone is revealed. It should be noted, however, that intact skeletal material and decalcified bone have entirely different mechanical properties. Olivo, Maj and Toajari ('37) considered that both the anisotropy exhibited by strength tests on bones and the directions of split lines were correlated with the resultant of the predominantly obliquely longitudinal orientation of the collagenous fibrillae in the lamellae of osteones. Dowgjallo ('32), Benninghoff ('25), and Siepel ('48) have shown splitline patterns for the human mandible. Siepel's study also includes data on anthropoid jaws; additional data on primate bones have been provided by Henckel ( '3 1 ) and by Tappan ('53, '54). The overall pattern and arrangement of vascular channels are well shown by our cleared, deorganified and ink infiltrated material. These vascular channels, for adult mandibles, are in turn correlated with the organization of the osseous component of the cylindrical Haversian systems of lamellae or osteones. No other known technique brings out as clearly the regional differences in vascular structure of a whole bone. Details such as channel angulation and diameter, regions of bone resorption, blind-end channels, local discontinuities and Volkmann canals may be seen when preparations are magnified. The method provides a quick means for detecting localized structural peculiarities and should become a valuable adjunct for evaluating experiment ally induced ch ariges in bone or alterations due to disease.