Figure 2 in The histology and affinities of sinacanthid fishes: primitive gnathostomes from the Silurian of China

Figure 2. Histology of sinacanthid spines. A, montage of a single transverse section; B, detail showing clear boundary (arrowed) between the outer layer of atubular dentine and lamellar dentine and the inner layer of globular calcified cartilage, note also the pulp cavities beneath each ridge; C, scanning electron micrograph of HCl etched section through ridge and globular calcified cartilage showing boundary (arrowed) between the outer layer and the inner layer; D, detail of globular atubular dentine; E, cross section through presumed juvenile spine ridge showing open pulp cavity; F, globular calcified cartilage lining vascular canal. All transmitted light micrographs using Nomarski interference optics unless otherwise stated. A–D, F, Sinacanthus wuchangensis P'an (1959) from the Tataaiertage Formation, Lower Silurian, Kalpin, Xinjiang, IVPP.V14325; E, Sinacanthus sp. from the Xiushan Formation, Lower Silurian, Shiqian, Guizhou Province, NIGP 139378. Abbreviations: ad, atubular dentine; pc, pulp cavity; ld, lamellar dentine; gcc, globular calcified cartilage; vc, vascular canal. Scale bars: A = 500 Mm; B, C, E = 100 Mm; D, F = 50 Mm.