. The cat : an introduction to the study of backboned animals, especially mammals. Cats; Anatomy, Comparative. 32 THE CAT. [chap. II. and canaliculi. It is thinnest towards the cervix of each tooth, and thickens towards the apex of each fang, and there it may even contain vascular canals like the Haversian canals of bone tissue.* The Enamel is so mineralized a structure that it only contains about 3 J per cent, of animal matter, while it has 90 per cent, of phosphate of lime. It consists of a multitude of slender, solid, undulating, hexagonal rods, closely adjusted to each other, and about 5oV
. The cat : an introduction to the study of backboned animals, especially mammals. Cats; Anatomy, Comparative. 32 THE CAT. [chap. II. and canaliculi. It is thinnest towards the cervix of each tooth, and thickens towards the apex of each fang, and there it may even contain vascular canals like the Haversian canals of bone tissue.* The Enamel is so mineralized a structure that it only contains about 3 J per cent, of animal matter, while it has 90 per cent, of phosphate of lime. It consists of a multitude of slender, solid, undulating, hexagonal rods, closely adjusted to each other, and about 5oV0 of an inch in diameter. Each rod is attached by one end to a minute depression of the surface of the aentine, and thence extends outwards, its distal part being at right angles to the external surface of the enamel. § 20. We have seen that hair and claws are epidermic dermal appendages, but teeth are appendages of the dermis. They are not altogether so, however; for though the dentine is formed by ossification of a process of the corium, and cement by calcifi- cation of the connective tissue surrounding that papilla, yet the enamel has a different, and indeed an epidermal origin. It is formed from a depression of the epithelium of the gum, which dips in till it becomes applied to the apex of the rising dermal papilla, which last is destined, by its calcification, to form the bulk of the tooth. Having thus applied itself to invest the crown of the nascent tooth, it calcifies and so be- comes the enamel. Thus each tooth has a double nature. By its dentine and cement it is dermal, but its enamel is a modification of the epi- dermis. Each permanent tooth takes its origin in a cavity of the jaw, placed just behind the milk-tooth it is destined to succeed. A little process from the inflected epi- thelium (or " enamel organ ") which forms the enamel of the milk-tooth, is given off to invest the minute papilla which is to grow into the permanent tooth. As the new tooth is
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectanatomy, bookyear1881
