. The Cambridge natural history. Zoology. VERTEBRAL COLUMN 195 (Jiaemal arches) enclosing a haemal canal (Fig. 112, B). The apex of each arch is prolonged into a median process or haemal spine. Although not recognisable in the Dog-Fish, paired inter-ventral cartilages, corresponding with the inter-dorsals above, are present in some Elasmobranchs and alternate with the basi-ventrals. In the caudal region of others ( Skates and Piays) ventral counterparts of the supra-interdorsals are present, and are termed infra-ventral cartilages. Much in the same way that their dorsal equivalents enclose
. The Cambridge natural history. Zoology. VERTEBRAL COLUMN 195 (Jiaemal arches) enclosing a haemal canal (Fig. 112, B). The apex of each arch is prolonged into a median process or haemal spine. Although not recognisable in the Dog-Fish, paired inter-ventral cartilages, corresponding with the inter-dorsals above, are present in some Elasmobranchs and alternate with the basi-ventrals. In the caudal region of others ( Skates and Piays) ventral counterparts of the supra-interdorsals are present, and are termed infra-ventral cartilages. Much in the same way that their dorsal equivalents enclose a neural canal, so the ventral arcualia partially surround the viscera-containing coelom in the trunk; and in the tail, but more completely, the vestigial coelom g^. of that region or the haemal canal. The different vertebral compon- ents are by no means of equal morphological value. The basi- dorsals and basi- ventrals, and the inter-dorsals and inter-ventrals, are the primary elements and the most important. The supra-dorsals are merely cartilages segmented off from the basi-dorsals and inter- dorsals, while the ribs and the infra-ventrals are similarly derived from the basi-ventrals and inter-ventrals respectively. As to the vertebral elements which collectively form a vertebra in the Dog- Fish, it would seem from evidence afforded by the neuromeres,"' and more especially by the facts of development, that each complete skeletal segment or vertebra consists of a pair of basi-dorsals with the preceding pair of inter-dorsals, and of a pair of basi-ventrals with the next succeeding pair of inter-ventrals. It must be emphasised, however, that, considered as a joint or segment in a flexible back-bone, a vertebra is a physiological unit, the morpho- logical value of which may differ widely in different Fishes. Hence, in other Fishes, the grouping of vertebral components to ^ Neuromeres are body-segments defined and limited by the of the suc- cessive pairs of spinal ner
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
