. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. 364 ANATOMY OF VERTEBRATES. 241 a fissure, into which a thin outer layer of cement, fig. 244, c, is reflected into the body of the tooth, following the sinuous wavings of the lobes of dentine, d, which diverge from the central pulp-cavity, a. The inflected fold of cement, c, runs straight for about half a line, and then becomes wavy, the waves rapidly in- creasing in breadth as they recede from the periphery of the tooth; the first two, three, or four undulations are simple ; then their contour itself becomes broken by s
. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. 364 ANATOMY OF VERTEBRATES. 241 a fissure, into which a thin outer layer of cement, fig. 244, c, is reflected into the body of the tooth, following the sinuous wavings of the lobes of dentine, d, which diverge from the central pulp-cavity, a. The inflected fold of cement, c, runs straight for about half a line, and then becomes wavy, the waves rapidly in- creasing in breadth as they recede from the periphery of the tooth; the first two, three, or four undulations are simple ; then their contour itself becomes broken by smaller or secondary waves these become stronger as the fold ap- proaches the centre of the tooth, when it increases in thickness, and finally terminates by a slight dilatation or loop close to the pulp-cavity, from which the free margin of the inflected fold of cement is separated by an extremely thin laj^er of dentine. The number of the inflected converrrino; folds of dentine is about fifty at the middle of the crown of the tooth figured, but is greater at the base. All the inflected folds of cemeut at the base of the tooth have the same complicated disposition with increased extent; but, as they approach their ter- mination towards the upper part of the tooth, they also gradually diminish in breadth, and consequently penetrate to a less distance into the substance of the tooth. Hence, in such a section as is delineated, fig. 244, it will be observed that some of the convo- luted folds, as those marked c, extend near to the centre of the tooth; others, as those marked c', reach only about half way to the centre ; and those folds, c", which, to use a geological ex- pression, are ' cropping out,' penetrate to a very short distance into the dentine, and resemble, in their extent and simplicit}^ the converginc; folds of cement in the fanirs of the tooth of tlie Ichthyosaurus and Lepidostcns. The disposition of the dentine is still more complicated than that of the cement. It
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